TWI872070B - Apparatus comprising an electrostatic clamp and method - Google Patents

Abstract

An apparatus comprising an electrostatic clamp for clamping a component, and a mechanism for generating free charges adjacent to the electrostatic clamp. The electrostatic clamp comprises an electrode or a plurality of electrodes. The apparatus is configured to: operate in a first mode in which the or each electrode is set at a potential such that clamping electric fields are generated between the electrostatic clamp and the component to clamp the component, operate in a second mode in which the or each potential of the or each electrode is set such that the component is unclamped, and operate in a third mode in which the or each potential of the or each electrode is set such that the flux of free charges generated by the mechanism to a surface of the component adjacent to the electrostatic clamp is increased in comparison with operating in the first or second mode.

Description

Apparatus and method including electrostatic clamps

The present invention relates to an apparatus including an electrostatic chuck, and a method of operating the same. More particularly but not exclusively, the apparatus may include a lithography apparatus, the electrostatic chuck being configured to hold components such as patterned devices during lithography patterning.

A lithography apparatus is a machine constructed to apply a desired pattern to a substrate. A lithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithography apparatus can, for example, project a pattern at a patterned device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate.

To project a pattern onto a substrate, a lithography apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be formed on the substrate. Lithography apparatus using extreme ultraviolet (EUV) radiation having a wavelength in the range of 4nm to 20nm (e.g. 6.7nm or 13.5nm) can be used to form smaller features on a substrate than lithography apparatus using radiation having a wavelength of, for example, 193nm.

Lithography equipment may often use high voltage electrostatic chucks to, for example, hold patterned devices during patterning operations. The electrostatic chuck and patterned devices are often maintained in a low voltage, hydrogen-rich environment. This environment is non-conductive. Therefore, it is understood that charge can accumulate on dielectric surfaces or ungrounded surfaces. For example, during operation, charge can accumulate on dielectric surfaces or ungrounded surfaces by touching parts (such as a mask chuck) or by particle collisions during gas flow.

It should also be understood that EUV radiation can cause a hydrogen-rich environment to become conductive due to the generation of EUV-induced hydrogen plasma. Free charges generated within the EUV-induced hydrogen plasma can be attracted to (or repelled by) the electric fields generated by the electrostatic fixture. On the other hand, in the absence of EUV-induced plasma or in a region that is at a distance from or well shielded from any EUV-induced plasma, charges can accumulate on dielectric or ungrounded surfaces and can continue to exist after any electric fields have been removed.

In addition to charge buildup, very strong electrostatic fields (e.g., about ~1 kV/cm to 100 kV/cm) can be generated between parts of the electrostatic fixture and other system components. Specifically, the high voltage applied to the electrodes of the electrostatic fixture causes nearby conductors (e.g., conductive coatings that may be present on the surface of the mask) to polarize. As a result, strong electrostatic fields are generated, especially at sharp features (e.g., the edges of conductive mask coatings).

According to a first aspect of the present invention, there is provided an apparatus comprising: an electrostatic clamp for clamping a component; and a mechanism for generating free charge adjacent to the electrostatic clamp: wherein the electrostatic clamp comprises an electrode or a plurality of electrodes, wherein the apparatus is configured to: operate in a first mode, in which the electrode or each of the plurality of electrodes is set at an electric potential so that a clamping electric field is generated between the electrostatic clamp and the component to clamp the component. holding the assembly; operating in a second mode in which the potential of the electrode or each of the plurality of electrodes is set such that the assembly is released; and operating in a third mode in which the potential of the electrode or each of the plurality of electrodes is set such that the flux of free charge generated by the mechanism to a surface of the assembly adjacent to the electrostatic clamp is increased compared to operating in the first or second mode.

This enables accelerated residual charge neutralization during reticle unloading. Thus, compensation of residual charge on the reticle by EUV-induced plasma during reticle unloading/loading actions can be enhanced. This avoids electrical collapse, which can lead to indirect reticle surface damage. In addition, yield-neutral reticle grounding can be achieved.

The electrostatic fixture may include the plurality of electrodes, and wherein in the third mode, the apparatus may be configured such that the potential of an edge electrode closest to an edge of the electrostatic fixture is set to positive. This may provide an additional negative bias to the second surface of the zoom mask (i.e., the surface adjacent to the fixture), which increases the positive ion flux toward the zoom mask MA.

In the third mode, the apparatus may be configured so that the or each potential of the electrode or each of the plurality of electrodes is set so that the potential of the electrode or the average potential of the plurality of electrodes is negative. This may capacitively induce a negative potential on the multiplication mask which attracts positive ions towards the second surface of the multiplication mask.

In the third mode, the device can be configured so that the potentials of the plurality of electrodes are set so that the average potential of the plurality of electrodes is substantially 0 V. This means that the capacitively induced potential on the zoom mask (particularly on the second surface of the zoom mask) remains unchanged.

The electrostatic fixture may include the plurality of electrodes, and wherein in the third mode, the apparatus may be configured such that the potential of an edge electrode closest to an edge of the electrostatic fixture is set to be negative, and the potential of the remaining portion of the plurality of electrodes is set such that the average potential of the plurality of electrodes has a less negative value than the potential of the edge electrode.

In the third mode, the apparatus may be configured so that the or each potential of the electrode or each of the plurality of electrodes is set so that the surface of the component adjacent to the electrostatic fixture has a positive potential before the component is freed from the electrostatic fixture to be spaced apart from the electrostatic fixture. This means that the neutralization of the residual charge of the zoom mask during unloading can be achieved by electrons (rather than by positive ions), so neutralization is achieved more quickly.

In the third mode, the potential of the electrode or the average potential of the electrodes can be set to a predetermined negative value so that during the period when the component is moved from being clamped by the electrostatic clamp to being separated from the electrostatic clamp, the surface of the component has a potential substantially the same as the potential of the electrode or the average potential of the electrodes. This can prevent the zoom mask from being charged during exposure.

In the third mode, the potential of the electrode or the average potential of the electrodes may be set to the predetermined negative value so that after the assembly is exposed, the assembly has substantially zero charge. This may mean that during unloading, the potential difference between the second surface of the zoom mask and the clamping surface of the clamp does not increase relatively significantly.

In the third mode, the or each potential of the electrode or each of the plurality of electrodes may be set for at least one of: a period of time before the component moves from being clamped by the electrostatic clamp to being separated from the electrostatic clamp; a portion or all of the time it takes for the component to move from being clamped by the electrostatic clamp to being separated from the electrostatic clamp; and a portion or all of the time it takes for the component to move from being separated from the electrostatic clamp to being clamped by the electrostatic clamp.

In the third mode, the potential of the electrode or the average potential of the electrodes can be set during at least a portion or all of the time that the mechanism generates free charge.

The mechanism for generating free charge in proximity to the electrostatic fixture may include: a gas source; and an ionizing radiation source configured to ionize a gas provided by the gas source.

The ionizing radiation source may include at least one of an EUV source, a VUV source, a soft x-ray source, and a radioactive source.

The electrostatic fixture may comprise a further electrode or a plurality of further electrodes, wherein the further electrode or the plurality of further electrodes may be positioned at least partially around a volume extending from a surface of the component adjacent to the electrostatic fixture in the direction of the electrostatic fixture, wherein the apparatus may be configured so that the or each potential of the or each further electrode is set so that the flux of free charges generated by the mechanism to the surface of the component adjacent to the electrostatic fixture is reduced.

The apparatus may be configured to: measure charge or current from a voltage supply to the electrode or each of the plurality of electrodes using at least one charge or current measuring device; calculate capacitance of the electrode or each of the plurality of electrodes using the measured charge or current to the electrode or each of the plurality of electrodes; and determine a potential of a surface of the component adjacent to the electrostatic fixture using the calculated capacitance of the electrode or each of the plurality of electrodes.

The capacitance of the electrode or each of the plurality of electrodes may be calculated using at least one measuring device. The apparatus may include at least one measuring device. The apparatus may include at least one charge measuring device. The apparatus may include at least one current measuring device.

According to a second aspect of the present invention, a lithography apparatus configured to project a pattern from a patterned device onto a substrate is provided, wherein the lithography apparatus comprises an illumination system configured to adjust a radiation beam and an apparatus as described above, wherein the illumination system is configured to project the radiation beam onto the patterned device, and wherein the patterned device comprises a component to be clamped, wherein the lithography apparatus comprises an apparatus as described above.

According to a third aspect of the present invention, a method for operating an apparatus is provided, the apparatus comprising: an electrostatic fixture; and a mechanism for generating free charge adjacent to the electrostatic fixture, the electrostatic fixture comprising an electrode or a plurality of electrodes, the method comprising: providing a component adjacent to the electrostatic fixture; controlling the mechanism for generating free charge to generate free charge adjacent to the electrostatic fixture; operating the apparatus in a first mode, in which the electrode or each of the plurality of electrodes is set to a potential A clamping electric field is generated between the electrostatic clamp and the component to clamp the component; the device is operated in a second mode, in which the potential of the electrode or each of the plurality of electrodes is set so that the component is released; and the device is operated in a third mode, in which the potential of the electrode or each of the plurality of electrodes is set so that the flux of free charges to a surface of the component adjacent to the electrostatic clamp is increased compared to operation in the first or second mode.

The electrostatic fixture may include a plurality of electrodes, and the method may further include: in the third mode, setting the potential of an edge electrode closest to an edge of the electrostatic fixture to positive.

The method may further include: in the third mode, setting the potential of the electrode or each of the plurality of electrodes so that the potential of the electrode or the average potential of the plurality of electrodes is negative.

The method may further include: in the third mode, setting the potentials of the plurality of electrodes so that the average potential of the plurality of electrodes is substantially 0V.

The electrostatic fixture may further include a further electrode or electrodes, the further electrode or electrodes being positioned at least partially around a volume, the volume extending from a surface of the component adjacent to the electrostatic fixture in the direction of the electrostatic fixture. The method may further include: setting the or each potential of the or each further electrode so that the flux of free charges to the surface of the component adjacent to the electrostatic fixture is reduced.

The method may further include: measuring charge or current from a voltage supply to the electrode or each of the plurality of electrodes using at least one charge or current measuring device; calculating the capacitance of the electrode or each of the plurality of electrodes using the measured charge or current to the electrode or each of the plurality of electrodes; and determining the potential of a surface of the component adjacent to the electrostatic fixture using the calculated capacitance of the electrode or each of the plurality of electrodes.

According to a fourth aspect of the present invention, a device is provided, comprising: an electrostatic fixture for clamping a component; and a mechanism for generating free charges adjacent to the electrostatic fixture: wherein the electrostatic fixture comprises an electrode or a plurality of electrodes, wherein the electrode or the plurality of electrodes are positioned at least partially around a volume, the volume extending from a surface of the component adjacent to the electrostatic fixture in the direction of the electrostatic fixture, wherein the device is configured so that the or each potential of each of the electrode or the plurality of electrodes is set so that the flux of free charges generated by the mechanism to the surface of the component adjacent to the electrostatic fixture is reduced.

This may have the advantage of preventing or at least reducing charging of the reticle. This may avoid electrical breakdown (e.g. during reticle unloading) which could lead to indirect reticle surface damage.

The electrode or electrodes may be located on one side of the component.

The electrode or electrodes may extend all the way around the volume.

The or each potential of the electrode or each of the plurality of electrodes may be set to negative.

The or each potential of the electrode or each of the plurality of electrodes may be set to positive.

The electrode or each of the plurality of electrodes may be in electrical contact with the surface of the component adjacent to the electrostatic fixture.

At least one or more edges of the surface of the electrode or each of the plurality of electrodes adjacent to the component may be rounded.

The electrode or each of the plurality of electrodes may be rounded in regions corresponding to corners of the assembly.

The or each potential of the electrode or each of the plurality of electrodes may be set within at least one of the following times: at least a portion or all of the time that the mechanism generates free charge, and a period of time before the component moves from being clamped by the electrostatic clamp to being separated from the electrostatic clamp.

The mechanism for generating free charge in proximity to the electrostatic fixture may include: a gas source; and an ionizing radiation source configured to ionize a gas provided by the gas source.

The ionizing radiation source may include at least one of an EUV source, a VUV source, a soft x-ray source, and a radioactive source.

According to a fifth aspect of the present invention, a lithography apparatus configured to project a pattern from a patterned device onto a substrate is provided, wherein the lithography apparatus comprises an illumination system configured to adjust a radiation beam and an apparatus as described above, wherein the illumination system is configured to project the radiation beam onto the patterned device, and wherein the patterned device comprises a component to be clamped, wherein the lithography apparatus comprises an apparatus as described above.

According to a sixth aspect of the present invention, a method of operating an apparatus is provided, the apparatus comprising: an electrostatic fixture; and a mechanism for generating free charge adjacent to the electrostatic fixture, the electrostatic fixture comprising an electrode or electrodes, the electrode or electrodes being positioned at least partially around a volume, the volume being oriented in a direction from the electrostatic fixture to the electrostatic fixture. The method comprises: providing a component adjacent to the electrostatic fixture; controlling the mechanism for generating free charge to generate free charge adjacent to the electrostatic fixture; setting the potential of the electrode or each of the plurality of electrodes so that the flux of free charge to the surface of the component adjacent to the electrostatic fixture is reduced.

The method may further comprise setting the potential of the electrode or each of the plurality of electrodes to negative.

The method may further comprise setting the or each potential of the electrode or each of the plurality of electrodes to be positive.

The method may further include controlling the potential of the surface of the component adjacent to the electrostatic fixture via an electrical connection between the electrode or each of the plurality of electrodes and the surface of the component adjacent to the electrostatic fixture.

According to a seventh aspect of the present invention, there is provided an apparatus comprising: an electrostatic fixture for holding a component; and a mechanism for generating free charge adjacent to the electrostatic fixture: wherein the electrostatic fixture comprises an electrode or a plurality of electrodes, wherein the apparatus is configured to: use at least one charge or current measuring device to measure a charge or current from a voltage supply charge or current to the electrode or each of the plurality of electrodes; calculating the capacitance of the electrode or each of the plurality of electrodes using the measured charge or current to the electrode or each of the plurality of electrodes; and determining the potential of a surface of the component adjacent to the electrostatic fixture using the calculated capacitance of the electrode or each of the plurality of electrodes.

This may have the advantage of providing reliable control of the potential of the surface of the assembly in close proximity to the electrostatic fixture. This may have the advantage of preventing or at least reducing charging of the reticle. This may avoid electrical collapse (e.g. during unloading of the reticle) leading to indirect reticle surface damage.

The capacitance of the electrode or each of the plurality of electrodes may be calculated using at least one measuring device. The apparatus may include at least one measuring device. The apparatus may include at least one charge measuring device. The apparatus may include at least one current measuring device.

The apparatus may be configured so that the potential of the or each of the plurality of electrodes is set so that the potential of a surface of the component adjacent to the electrostatic fixture is substantially a predetermined value.

The predetermined value of the potential of the surface of the component adjacent to the electrostatic fixture may be at least one of positive, negative, and substantially zero.

The device can be configured to measure the ratio of the capacitances of the plurality of electrodes.

The device may be configured to set the potential of at least one of the plurality of electrodes based on the ratio of the capacitances of the plurality of electrodes.

The apparatus may be configured to set the potential of at least one of the plurality of electrodes based on a variance in capacitance of the electrode or each of the plurality of electrodes.

The apparatus may be configured to change the potential of the plurality of electrodes by a predetermined amount in a stepwise manner and to use the at least one charge or current measuring device to measure the charge or current from the voltage supply to the electrode or each of the plurality of electrodes after each potential change for determining the individual capacitances of the plurality of electrodes.

The potential of the electrode or each of the plurality of electrodes may be set within at least one of the following times: before the mechanism generates free charge, at least a portion of the time, or all of the time; and before the component moves from being clamped by the electrostatic fixture to being separated from the electrostatic fixture.

The mechanism for generating free charge in proximity to the electrostatic fixture may include: a gas source; and an ionizing radiation source configured to ionize a gas provided by the gas source.

The ionizing radiation source may include at least one of an EUV source, a VUV source, a soft x-ray source, and a radioactive source.

According to an eighth aspect of the present invention, a lithography apparatus configured to project a pattern from a patterned device onto a substrate is provided, wherein the lithography apparatus comprises an illumination system configured to adjust a radiation beam and an apparatus as described above, wherein the illumination system is configured to project the radiation beam onto the patterned device, and wherein the patterned device comprises a component to be clamped, wherein the lithography apparatus comprises an apparatus as described above.

According to a ninth aspect of the present invention, a method for operating an apparatus is provided, the apparatus comprising: an electrostatic fixture; and a mechanism for generating free charge adjacent to the electrostatic fixture, the electrostatic fixture comprising an electrode or a plurality of electrodes, the method comprising: providing a component adjacent to the electrostatic fixture; controlling the mechanism for generating free charge to generate free charge adjacent to the electrostatic fixture; using at least A charge or current measuring device measures charge or current from a voltage supply to the electrode or each of the plurality of electrodes; calculates capacitance of the electrode or each of the plurality of electrodes using the measured charge or current to the electrode or each of the plurality of electrodes; and determines a potential of a surface of the component adjacent to the electrostatic fixture using the calculated capacitance of the electrode or each of the plurality of electrodes.

The method may further include setting the potential of the or each of the plurality of electrodes so that the potential of a surface of the component adjacent to the electrostatic fixture is substantially a predetermined value.

The method may further include setting the potential of the or each of the plurality of electrodes so that the predetermined value of the potential of the surface of the component adjacent to the electrostatic fixture is at least one of positive, negative and substantially zero.

The method may further include setting the potential of at least one of the plurality of electrodes based on a ratio of the capacitances of the plurality of electrodes.

The method may further include setting the potential of at least one of the plurality of electrodes based on a variance in the capacitance of the electrode or each of the plurality of electrodes.

According to a tenth aspect of the present invention, a computer program is provided, which includes computer-readable instructions configured to cause a processor to perform a method as described above. This has the advantage of not requiring additional hardware.

According to an eleventh aspect of the present invention, a computer-readable medium is provided, which carries a computer program as described above.

According to a twelfth aspect of the present invention, a computer device for operating a device is provided, which includes: a memory storing processor-readable instructions; and a processor configured to read and execute instructions stored in the memory; wherein the processor-readable instructions include instructions configured to control the computer to perform a method as described above.

10: Faceted field mirror device

11: Faceted pupil mirror device

13: Mirror

14: Mirror

100: Electrostatic clamp

102: generally flat clamping surface

104A: Electrode/Edge Electrode

104B: Electrode

104C: Electrode

104D: Electrode

122: First plane surface/front surface

124: Second plane surface/rear surface

126: Base plate

128: Reduction mask edge

200: Electrostatic clamp

202: Clamping surface

204A: Electrode

204B: Electrode

204C: Electrode

204D: Electrode

204E: Other electrode

204F: Side wall electrode

204G: Wall electrode

224: Second surface

228: Edge

230: Volume

232: Space

300A: Charge measurement device

300B: Charge measurement device

300C: Charge measurement device

300D: Charge measurement device

B: EUV radiation beam

B': Patterned EUV radiation beam

C1: Capacitor

C2: Capacitor

C3: Capacitor

C4: Capacitor

IL: Lighting system

LA: Lithography equipment

MA: Patterned device/reduction mask

MT: Support structure

PS: Projection system

SO: Radiation source

V1: voltage

V2: voltage

V3: voltage

V4: Voltage

W: Substrate

WT: Substrate table

Embodiments of the present invention will now be described with reference to the accompanying schematic drawings, by way of example only, in which: - FIG. 1 depicts a lithography system comprising a lithography apparatus and a radiation source; - FIGS. 2a to 2c depict an electrostatic fixture and a patterning device used in a lithography apparatus according to an embodiment of the present invention; - FIGS. 3a to 3c depict an electrostatic fixture and a patterning device used in a lithography apparatus according to an embodiment of the present invention; - FIGS. 4a to 4c depict an electrostatic fixture and a patterning device used in a lithography apparatus according to an embodiment of the present invention; - FIG. 5 depicts an electrostatic fixture and a patterning device used in a lithography apparatus according to an embodiment of the present invention; - FIG. 6 depicts a plan view of an electrostatic fixture and a patterning device used in a lithography device according to the embodiment of FIG. 5; - FIG. 6a depicts an electrostatic fixture and a patterning device used in a lithography device according to an embodiment of the present invention; - FIG. 7 depicts a plan view of an electrostatic fixture and a patterning device used in a lithography device according to an embodiment of the present invention; - FIG. 8 depicts a plan view of an electrostatic fixture and a patterning device used in a lithography device according to an embodiment of the present invention; - FIG. 9 depicts a plan view of an electrostatic fixture and a patterning device used in a lithography device according to an embodiment of the present invention; - FIG. 10 depicts a schematic circuit diagram of an electrostatic fixture and a patterning device used in a lithography device according to an embodiment of the present invention.

FIG1 shows a lithography system including a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and supply the EUV radiation beam B to the lithography apparatus LA. The lithography apparatus LA includes an illumination system IL, a support structure MT configured to support a patterned device MA (e.g., a mask or a reticle), a projection system PS, and a substrate table WT configured to support a substrate W.

The illumination system IL is configured to condition the EUV radiation beam B before the EUV radiation beam B is incident on the patterned device MA. In addition, the illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11. The faceted field mirror device 10 and the faceted pupil mirror device 11 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired angular distribution. In addition to or instead of the faceted field mirror device 10 and the faceted pupil mirror device 11, the illumination system IL may also include other mirrors or devices.

After being conditioned thus, the EUV radiation beam B interacts with the patterned device MA. As a result of this interaction, a patterned EUV radiation beam B' is generated. The projection system PS is configured to project the patterned EUV radiation beam B' onto the substrate W. For that purpose, the projection system PS may include a plurality of mirrors 13, 14 configured to project the patterned EUV radiation beam B' onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B', thereby forming an image with features that are smaller than corresponding features on the patterned device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is illustrated in FIG. 1 as having only two mirrors 13, 14, the projection system PS may include a different number of mirrors (e.g., six or eight mirrors).

The substrate W may include a previously formed pattern. In this case, the lithography apparatus LA aligns the image formed by the patterned EUV radiation beam B' with the pattern previously formed on the substrate W.

A relative vacuum, i.e. a small amount of gas (e.g. hydrogen) at a pressure sufficiently below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL and/or in the projection system PS.

The radiation source SO may be a laser produced plasma (LPP) source, a discharge produced plasma (DPP) source, a free electron laser (FEL) or any other radiation source capable of generating EUV radiation.

FIG. 2 a shows a cross section of the support structure MT in more detail. The cross section is in the x-plane, extending vertically in the z-direction and horizontally in the y-direction in the shown orientation. The y-direction can be considered as the scanning direction of the lithography apparatus and the x-direction can be considered as perpendicular to the scanning direction. The support structure MT comprises an electrostatic fixture 100 configured to clamp the patterned device MA during a lithography operation. The fixture 100 comprises a substantially planar clamping surface 102, and fixture electrodes A to D disposed within the fixture body. The electrodes 104A to 104D are separated from the clamping surface 102 of the fixture 100 by a dielectric coating. Nodules (not shown) may protrude from the clamping surface 102 and serve to separate the clamped patterned device MA from the clamping surface 102. The nodules may, for example, have a height of about 10 μm and may collectively cover about 1% of the surface of the fixture 100. It should be understood that many features of the fixture 100 (e.g., wiring, additional electrodes) are omitted for simplicity.

The fixture 100 may be considered as part of the lithography apparatus LA, or may be considered as part of an apparatus forming part of or separate from the lithography apparatus LA. The lithography apparatus LA or the apparatus may include a mechanism for generating free charges.

The patterned device MA is generally planar and has a first planar surface 122 and a second planar surface 124 that are opposite to each other. In use (e.g., as shown in FIG. 1 ), the first surface 122 is configured to reflect the radiation beam B and cause a pattern to be imparted to the beam B. Specifically, a region of the first surface 122 may be patterned so as to cause the radiation beam B to become patterned. The patterned region of the first surface 122 has a conductive coating. The first surface 122 may be referred to as the front face of the patterned device MA. That is, the front face of the zoom mask is the surface of the patterned device MA that faces away from the electrostatic fixture 100.

In order to enable the electrostatic fixture 100 to clamp the patterned device MA, the second surface 124 has a conductive coating that generally covers most of the second surface 124. The second surface 124 can be referred to as the back side of the patterned device MA. That is, the back side of the patterned device MA is the surface of the patterned device MA facing the electrostatic fixture 100. In other words, the back side of the patterned device MA is the surface of the patterned device MA adjacent to the electrostatic fixture 100.

A bottom plate 126 facing the first surface 122 of the patterned device MA is located on the opposite side of the electrostatic fixture 100. The bottom plate 126 is part of an exchange device for transferring the zoom mask MA to and from the lithography equipment LA. The bottom plate 126 is grounded and can be at a potential of substantially 0V.

It should be understood that the electrostatic clamp 100 can use a voltage of about several kV in order to clamp the patterned device MA. For example, the clamp 100 can be a bipolar electrostatic clamp, wherein the first subset 104A, 104C of electrodes 104A to 104D is connected to one or more voltage supplies (not shown) of about +1...10 kV (e.g., +2 kV), and the second subset 104B, 104D of electrodes 104A to 104D is connected to one or more voltage supplies of about -1...10 kV (e.g., -2 kV). Thus, a high electric field can be established between the clamp 100 and the patterned device MA, causing the patterned device MA to be attracted to the clamp 100. Specifically, charges are induced in a conductive coating region of the second surface 124 adjacent to the electrodes 104A to 104D, the region having an opposite sign to the applied voltage, and an attractive force is established between the opposing charges at various locations across the fixture 100 and the patterned device MA. The region of the fixture 100 configured to support the patterned device MA may be referred to as a support region. In addition, the region of the fixture 100 configured to generate a clamping force when the fixture 100 is operated to clamp the patterned device MA may be referred to as a clamping region.

The electrostatic chuck 100 can be operated in a first mode, in which the electrodes 104A to 104D are set to potentials such that a clamping electric field is generated between the electrostatic chuck 100 and the zoom mask MA to clamp the zoom mask MA. In this first mode, the electrodes 104A to 104D can be balanced, that is, the average potential of the electrodes 104A to 104D can be approximately 0 V. The electrostatic chuck 100 can be operated in a second mode, in which the electrodes 104A to 104D are set to potentials such that no or a relatively small clamping electric field is generated between the electrostatic chuck 100 and the zoom mask MA. For example, a minimum of 300V is usually required to overcome the weight of the zoom mask MA. Therefore, below 300V there will be no clamping. This value may vary depending on the quality of the clamping surface, so it may be 100V or 200V, etc. Therefore, in the second mode, the potential of the electrodes 104A to 104D is set appropriately and the zoom mask MA is released. In the second mode, the electrodes 104A to 104D may also be balanced, that is, the average potential of the electrodes 104A to 104D may be approximately 0V. The first and second modes of the operating fixture 100 may be considered normal operation.

The electrodes 104A to 104D each have a rectangular shape and are configured to be substantially parallel to each other. In this configuration, the four electrodes illustrated each span the width of the clamped patterned device MA in the x-direction and each cover approximately one quarter of the length of the patterned device MA in the y-direction. It should be understood that in other embodiments, a different number of electrodes may be used, such as 1, 2, 3, 5, 6, 7, 8 or more.

During normal operation of the fixture 100, an electric field will be established between the surface of the fixture 100 and the surface of the patterning device MA. In addition, due to the close separation between various charged surfaces (including other components within the lithography apparatus, such as (for example) shielding blades), electrostatic discharge can occur. That is, electrostatic discharge can occur between any charged surfaces, with the probability of discharge increasing as the electric field strength increases. Electrostatic discharge can damage components. Electrostatic discharge can generate particles from surfaces and can also release particles previously attached to surfaces within the lithography apparatus. It should be understood that this particle release is undesirable in the lithography apparatus because particles can land on critical areas of the apparatus, thereby potentially causing patterning defects in the processed substrate.

The high electric field generated by the electrostatic chuck strongly attracts any free charges. Free charges mean charges that are not bound to the physical substrate but are free to move according to the electric field lines (positive charges such as ions, or negative charges such as electrons). In addition, ample free charges are generated during EUV exposure. For example, electrons can be generated by photoemission and also from EUV-induced plasma, which is usually generated in the presence of hydrogen gas (which is often present in lithography tools). Positive ions can also be generated in EUV plasma.

The plasma generation process will now be discussed in more detail. It will be appreciated that the EUV photons within beam B will ionize hydrogen molecules, thereby generating _H2 ⁺ ions and free electrons. In the example using 13.5nm EUV radiation, each photon may have an energy of about 92eV, where the ionization energy of molecular hydrogen is about 15eV. Thus, the free electrons generated may have sufficient energy (e.g., >75eV) and range to generate a secondary plasma relatively far from the initial ionization event. Additionally, the electrons released in this manner (i.e., having an energy of about 75eV) may ionize one, two, or even three additional hydrogen molecules. Thus, even though the primary plasma is generated only at the point of EUV photon incidence, a secondary plasma may also be generated in the vicinity of the fixture.

In an embodiment, it will be appreciated that it is necessary to generate an EUV-induced plasma that provides a source of free charges in the vicinity of the patterned device MA.

In some embodiments, a secondary ionization source may be provided, thereby allowing plasma to be generated near the electrostatic chuck by components other than the EUV source SO. This configuration may reduce the overall output load of the EUV source SO. It should be understood that the embodiments described above may place additional demands on the EUV source SO by requiring additional EUV output compared to the EUV output required for imaging. In addition, in some embodiments, it is not possible for the EUV source to generate power continuously. Similarly, it is not possible and/or desirable for the EUV source to provide any EUV pulse energy in the range of 0% to 100% of the nominal output power while also ensuring clean collector operation and pulse energy stability.

Thus, in some embodiments, it may be preferable to provide an alternative mechanism for producing a region of increased gas conductivity relative to the primary EUV source.

For example, a source may be provided in proximity to the electrostatic clamp 100 and the clamped patterned device MA. A plurality of sources may be used. For example, the source may be a soft x-ray source or a VUV light source capable of operating at a pressure of less than 1 bar in a clean environment. The source may include a low power ionizer having a power of about 0.1 W to 1 W. In some embodiments, the source may include a radioactive source or an electron beam source.

In general, EUV sources SO and sources (which may, for example, include soft x-ray sources or VUV ionizers) may each be considered an example of an ionizing radiation source. In addition, such sources combined with hydrogen (or other) gas sources may be considered a mechanism for generating free charges. That is, a hydrogen plasma containing both positive ions and free electrons may be considered a free charge cloud. In addition, such free charges include both positive free charges and negative free charges.

A considerable voltage can be established between the fixture 100 and the patterned device MA after the patterned device MA is removed from the fixture 100.

It should be understood that capacitance exists between several components in the lithography apparatus LA. Specifically, the capacitance between the clamping surface 102 and the second surface 124 of the patterned device MA can be considered a variable capacitance that varies depending on the gap between the clamping surface 102 and the second surface 124. Similarly, the capacitance between the bottom plate 126 and the first surface 122 of the patterned device MA can be considered a variable capacitance that varies depending on the gap between the bottom plate 126 and the first surface 122.

It will be appreciated that in a closed system, with no charge being able to enter or leave the system and for a given initial charge state, any change in the separation between the fixture 100 and the patterned device MA and the separation between the patterned device MA and the base plate 126 will result in a change in the respective variable capacitance. Furthermore, this change in capacitance will also result in the voltage across the capacitance changing potentially significantly depending on the change in separation.

Specifically, the relationship Q=CV must always hold for each capacitor (assuming no charge is injected). Therefore, if the capacitance C changes and the amount of charge Q contained in that capacitor remains the same, the voltage V must change inversely proportional to the changed capacitance C. This can lead to a significant voltage amplification. The most significant change in voltage occurs at the back side of the patterned device MA, i.e. between the clamping surface 102 and the second surface 124 of the patterned device MA.

The resulting high voltages are understood to significantly increase the risk of discharge due to collapse of hydrogen gas in the vicinity of the electrostatic fixture 100 and the patterned device MA (e.g. due to the voltage at the surface of the patterned device MA exceeding the minimum Paschen limit of hydrogen, which is approximately 250 V).

Therefore, there is an electrostatic discharge opportunity within the lithography apparatus LA during unloading of the patterned device MA after clamping. Charge can become trapped at the dielectric surface of the clamp 100. In addition, residual charge can remain on the clamped patterned device MA once it has been released. As the loosened patterned device MA moves away from the clamp surface, the increased separation between the clamp surface and the patterned device surface can result in a decrease in capacitance and an increase in voltage. That is, given the proportional relationship between charge and voltage in a closed system (i.e., Q=C.V), any decrease in capacitance will result in a proportional increase in voltage as the capacitance changes (inversely proportional to the separation between the parallel plates). Therefore, when the patterned device MA is separated from the fixture 100, the voltage of the patterned device may be increased enough to cause an electrical collapse of the hydrogen gas. This discharge may cause damage to the patterned device MA, the electrostatic fixture 100 and/or particle generation, which may lead to subsequent defects.

The effect of the varying capacitance can be mitigated to some extent by introducing free charges during the unloading process. For example, a separate ionization source or indeed the EUV source SO can be used to generate a hydrogen plasma which provides the free charges (as described in detail above) and allows the fields established across the various dielectric components (and gaps) to be relaxed during the removal process.

Providing free charge can result in a significant reduction in the voltages built up between the various system components. That is, the electric fields built up by the high voltages can be compensated by introducing additional free charge. The source of these charges is effectively provided by the hydrogen plasma. The free charges within the plasma are driven by any electric fields as they begin to build up and cause them to collapse.

In this way, potential problems associated with building up significant voltage across the patterned device MA after removal from the electrostatic fixture 100 can be mitigated or avoided entirely. As mentioned above, it will be appreciated that this effect is not binary, and some (reduced strength) field may still be built up if insufficient charge is provided. However, it will be appreciated that even a reduction in voltage amplification (rather than a complete avoidance) may be beneficial, especially if the voltage is thereby always maintained below the lowest Paschen limit of hydrogen (approximately 250V).

Furthermore, free charges may be provided at various times during the separation of the fixture 100 and the patterned device MA. In practice, it will be appreciated that when the patterned device MA is clamped, free charges may have difficulty penetrating between adjacent surfaces. Thus, there may be an effective minimum separation for optimal provision of free charges.

Due to the residual charge accumulated on the front and back surfaces of the reticle during EUV radiation exposure and reticle handling (e.g. loading and unloading of the reticle), the reticle (patterned device) can suffer irreversible damage. As mentioned, this residual charge can lead to electrical collapse during reticle unloading, resulting in complete loss of the reticle. The reticle can be removed from the lithography equipment LA with a reticle potential of about 600V, which corresponds to a very large negative residual charge of about 50nC.

Due to EUV radiation, the reticle acquires charge, thereby generating fast electrons and charging the floating reticle surface to a small potential of about -10 V. Alternatively, the residual charge on the back of the reticle may be caused by tribocharging due to friction between the reticle surface and a fixture nodule made of a different material.

As mentioned, during reticle unloading, the capacitance of the reticle-fixture system decreases, which causes the potential on the back side of the reticle to increase to approximately -600 V. In some cases, this can cause electrical collapse to occur, resulting in indirect reticle surface damage.

The residual charge on the reticle BS also causes a high field between the reticle front and the base plate, which results in particle hopping from the base plate to the reticle FS during reticle handling in the scanner.

By using EUV-induced plasma as a charge source capable of reducing the reticle potential, grounding the reticle without the use of additional hardware can be achieved. However, providing, for example, 50 nC of charge carriers to the reticle back surface is limited by the amount of plasma generated by EUV radiation. Furthermore, the plasma density is reduced by the complex geometry of the environment surrounding the reticle and the hardware constraints associated with reticle unloading. Therefore, using EUV-induced plasma to achieve a scaled mask ground (i.e., soft ground) without additional assistance may have a yield loss, i.e., an increase in the time it takes for the substrate W to pass through the lithography apparatus LA, which is undesirable.

FIG. 2a shows the polarity and universal relative magnitude of the potential of the four electrodes 104A to 104D for the electrostatic chuck 100 operating in the third mode. That is, in one embodiment, electrodes 104A and 104D have positive potential (+), and electrodes 104B and 104C have negative potential (--, -), where the magnitude of electrode 104B is greater than the magnitude of the other electrodes. This means that the average potential of all electrodes 104A to 104D is negative.

The patterned device MA has an edge 128 (or end) which in this embodiment is closest to the EUV radiation beam B and therefore closest to the EUV-induced plasma. The electrode 104A may be referred to as an edge electrode. In this embodiment, the edge electrode 104A has a positive potential, as mentioned above.

The electrodes 104 to 104D are set to these potentials before EUV radiation is turned on to generate plasma. In the absence of plasma, the reticle MA will float and since the average potential of all electrodes 104A to 104D is negative and the bottom plate 126 is on the other side of the reticle MA, there will be a capacitively induced negative potential on the reticle MA. For example, the bottom plate 126 may be at approximately 0V, the fixture 100 may be at approximately -1000V, and therefore the reticle MA may be at approximately -900V due to the capacitive induced current. Since the second surface 124 of the multiplication mask MA is closer to the fixture 100 having a negative potential, the second surface 124 will have a less negative value than the first surface 122 of the multiplication mask MA. In other embodiments, the base plate does not need to be in place, and in other embodiments, the base plate can be exchanged with a different component. In other embodiments, the electrodes can be set to these potentials when EUV radiation is already turned on, that is, during plasma generation.

This electrode configuration provides increased positive ion flux to the second surface 124 of the patterned device MA while suppressing positive ion flux to the clamping surface 102 (and other clamping surfaces) of the fixture 100. The configuration of electrodes 104A-104D provides a positive near field at the edge 128 of the zoom mask and provides additional negative bias to the second surface 124 of the zoom mask MA (i.e., the surface adjacent to the fixture 100), which enhances the positive ion flux toward the zoom mask MA. This is because the electrode 104A at the edge 128 is positive and therefore pushes the positive ions away from the fixture 100 toward the zoom mask MA, and also because the capacitively induced potential on the zoom mask MA from the overall average negative potential of the electrodes 104A to 140D attracts the positive ions toward the second surface 124 of the zoom mask MA. Since the second surface 124 has a less negative value than the first surface 122, the positive ion flux will be attracted more to the second surface 124.

It should be understood that the electrostatic fixture 100 is operated in the third mode in the sense that the electrodes 104A to 104D have a potential that increases the flux of positive ions to the doubling mask MA compared to normal operation of the electrostatic fixture 100 (i.e., operation in the first or second mode). Previously, the fixture would not have been set to have an overall average negative or positive potential of the electrodes, and therefore the flux of free charges (electrons or ions) to the doubling mask would not have increased significantly when EUV radiation was turned on. Furthermore, it should be understood that the third operating mode of the electrostatic fixture 100 may include operating the electrostatic fixture 100 to clamp the doubling mask MA and/or operating the electrostatic fixture to not clamp the doubling mask MA.

FIG. 2b and FIG. 2c show the electrostatic chuck 100 operating in the third mode, which has a similar electrode configuration with a positive edge electrode 104A and the average potential of electrodes 104A to 104D being negative. However, in FIG. 2b, electrode 104C has a positive potential and electrodes 104B and 104D have negative potentials. The magnitude of the potential of electrode 104B is still greater than the magnitude of the potentials of the other electrodes. In FIG. 2c, electrode 104B has a positive potential and electrodes 104C and 104D have negative potentials, wherein the magnitude of the potential of electrode 104C is greater than the magnitude of the potentials of the other electrodes.

Such configuration of electrodes 104A to 104D, and more specifically, the specific configuration of voltages applied to electrodes 104A to 104D, enables acceleration of residual charge neutralization during unloading of the zoom mask MA. The acceleration is achieved by using electrodes 104A to 104D as additional E-field sources to provide higher plasma flux toward the zoom mask MA surface. That is, the electrostatic fixture 100 electrode 104A to 104D voltages are set in such a way that net positive charges from the plasma will be attracted to the (primary) rear surface 124 and the (secondary) front surface 122 of the zoom mask MA.

Therefore, the compensation of residual charge on the zoom mask MA by the plasma induced by EUV during the unloading/loading operation of the zoom mask MA can be enhanced.

Other advantages may be: No hardware changes are required, which saves on product costs and reduces development time. The implementation can be realized on any lithography equipment LA. In addition, the implementation can be customized for specific and unusual magnification mask MA conditions (such as the use of trimmed back-coated magnification masks MA). In addition, the contactless grounding solution can increase the life of the fixture 100/magnification mask MA.

Figures 3a to 3c show another embodiment of the electrostatic chuck 100 operating in the third mode, in which the common relative values of the polarity and potential of the four electrodes 104A to 104D are identified.

In the embodiment of FIG. 3a, each of electrodes 104A to 104D has a negative potential, wherein the magnitude of the potential of electrodes 104B to 104D is greater than the magnitude of the potential of electrode 104A (edge electrode). This means that the average potential of all electrodes 104A to 104D is still negative. Edge electrode 104A is negative, but the average potential of all electrodes has a less negative value than edge electrode 104A. This electrode configuration provides increased flux to the second surface 124 of the multiplication mask MA while suppressing flux to the fixture surface 102.

Therefore, a similar approach can be applied to achieve a <0 (negative) capacitively induced potential on the zoom mask MA by applying a net additional negative bias to electrodes 104B to 104D and combinations thereof. The configuration of electrodes 104A to 104D provides a near field at the zoom mask edge 128 that has a larger negative value than the rest of the zoom mask MA second surface 124 and provides an additional negative bias to the zoom mask MA second surface 124 (i.e., the surface adjacent to the fixture 100), which enhances the positive ion flux toward the zoom mask MA. This can also be achieved via an imbalance in the potential on the positive electrode.

Figures 3b and 3c show the electrostatic chuck 100 operating in a third mode, having a similar electrode configuration with a negative edge electrode 104A and the average potential of electrodes 104A to 104D having a less negative value. However, in Figure 3b, electrodes 104B and 104D have positive potentials and the potential of electrode 104C is negative and has a much larger magnitude of potential than the other electrodes. The embodiment of Figure 3c is the same as the embodiment of Figure 3b, except that the potentials of electrodes 104B and 104C have been swapped.

When the reticle MA is released and while the reticle MA is still held by the fixture 100, the unbalanced electrode potential can be applied before the EUV radiation beam B is “turned on”. Thus, embodiments achieve grounding of the reticle MA while the reticle MA is still on the electrostatic fixture 100, which grounds the reticle MA before the release action is initiated and thus minimizes the risk of damage to the reticle MA due to discharge. The residual charge of the reticle MA can be brought to zero while the reticle MA is still close to the fixture 100, or even still physically connected to the fixture 100. Thus, the risk of damage to the magnified mask MA due to discharge when the gap between the magnified mask MA and the fixture 100 becomes too large during unloading is significantly minimized (in the presence of a fixed charge, when the capacitance is reduced by increasing the gap, the voltage increases).

Figures 4a to 4c show another embodiment of the electrostatic chuck 100 operating in the third mode, in which the common relative values of the polarity and potential of the four electrodes 104A to 104D are identified.

In the embodiment of FIG. 4a, edge electrode 104A is positive, as in FIGS. 2a to 2c, but other electrodes 104B to 104D have potentials and magnitudes of potentials such that the average potential of all electrodes 104A to 104D is substantially 0 V. More specifically, electrodes 104A and 104D have positive potentials (+) and electrodes 104B and 104C have negative potentials (-), wherein the magnitude of the potential of each of the electrodes 104A to 104D is substantially the same.

Therefore, the capacitively induced potential on the zoom mask MA (particularly on the second surface 124) remains unchanged. The edge electrode 104A (which has a positive potential in this case) protects the fixture 100 from attracting positive ions and thereby increases the positive ion flux to the second surface 124 of the zoom mask MA, and protects the fixture nodules (not shown in the figure) from sputtering. This helps to maintain a relatively long life of the fixture functionality. Even though in this embodiment, the capacitively induced potential on the zoom mask MA is substantially 0V, the positive ion flux to the zoom mask MA is also increased when the positive ions are directed away from the fixture 100 by the positive edge electrode 104A.

The configuration of electrodes 104A to 104D provides a positive near field at the doubling mask edge 128, thereby enhancing the positive ion flux toward the doubling mask MA while maintaining zero additional bias to the doubling mask MA second surface 124.

FIG. 4b and FIG. 4c show the electrostatic chuck 100 operating in a third mode, having a similar electrode configuration with a positive edge electrode 104A and the average potential of electrodes 104A to 104D being substantially 0V. However, in FIG. 4b, electrodes 104B and 104D have negative potentials and electrode 104C is positive. The magnitude of the potential of each of electrodes 104A to 104D is substantially the same as in FIG. 4a. The embodiment of FIG. 4c is the same as the embodiment of FIG. 4b, except that the potentials of electrodes 104B and 104C have been swapped.

The embodiments of FIG. 4a to FIG. 4c create conditions for plasma flux (positive ions) mainly toward the second surface 124 of the magnification mask MA, while suppressing the positive ion flux toward the fixture 100. The main purpose is to minimize damage to the fixture surface 102 (and other fixture surfaces).

It should be understood that the exact configuration of electrodes 104A to 104D in Figures 2a to 4c described above is merely exemplary and in other embodiments, they may have different polarities and magnitudes as long as they provide the described advantages. For example, in Figure 4c, the polarities of electrodes 104B, 104C may be swapped and the magnitudes of the potentials of these electrodes 104B, 104C may both be increased to be substantially greater than electrodes 104A, 104D as long as the magnitudes substantially match. In this case, there will still be an edge electrode 104A with a positive potential and the overall average potential of the electrodes is substantially 0V.

Modeling of the plasma flux to the zoom mask MA can demonstrate the positive ion flux to the zoom mask MA second surface 124, thereby achieving charge compensation in just a fraction of a second (e.g., about 0.1s). This enables a yield-neutral realization of a soft ground of the zoom mask MA.

The embodiment can result in a neutralization of the residual charge on the second surface 124 of the zoom mask MA by a factor of about 10, thereby enabling a yield-neutral realization of soft zoom mask grounding during unloading (and loading) of the zoom mask MA.

Another embodiment is to set the electrostatic chuck 100 to operate in a third mode so that the electrodes 104A to 104D have an average negative potential before the patterned device (reduction mask) MA is exposed (i.e., when the radiation beam B is incident on the patterned device MA, thereby providing the reflected patterned EUV radiation beam B' onto the substrate). For example, the electrodes 104A to 104D can be set to have the same potential as in Figures 2a to 2c or Figures 3a to 3c or another configuration in which the average potential of the electrodes 104A to 104D is negative.

This approach aims to induce positive charge on the reticle MA (particularly the reticle MA second surface 124) so that the residual charge neutralization of the reticle MA during unloading will be achieved by electrons (rather than by positive ions as in the previous embodiment). This takes advantage of the higher mobility of electrons compared to that of ions, so neutralization is achieved faster (several orders of magnitude faster, i.e., neutralization can be achieved in only 0.1 s instead of 10 s). This approach can also achieve rapid neutralization of the back-trimmed reticle MA. This is because the back-trimmed reticle is neutralized more slowly due to the removal of about 1 mm of metal coating on the back of the reticle at the edge. The ion flux of the trimmed back coating has to pass through a narrow gap - namely, the space between the fixture and the back of the multiplication mask. The chance that ions can penetrate into this gap is relatively low, while this is not a problem for electrons. For example, a 2mm retraction of the coating will result in an indefinite back neutralization by ions, but by electrons it will still be completed in just a few seconds.

For example, in order to induce a positive charge on the reticle MA during exposure, the fixture electrodes 104A to 104D are set to provide a negative reticle MA offset potential of about -1 ... -100 V before exposure. Once the exposure is stopped, that is, once the EUV radiation beam B is no longer incident on the patterned device MA, the reticle MA will have a positive charge (rather than a negative charge as described above). To achieve this, one or more negative electrodes are set to a higher potential than the positive electrodes. For example, two positive electrodes are set to positive +1 kV and two negative electrodes are set to negative -1.1 kV. As a result, electrons will be repelled from the doubling mask MA and positive ions will be attracted to the doubling mask MA, thereby providing positive charge on the doubling mask MA after exposure.

The residual charge of the zoom mask MA can be brought to zero while the zoom mask MA is still close to the fixture 100, or even still physically connected to the fixture 100. Thus, the risk of damage to the zoom mask MA due to discharge when the gap between the zoom mask MA and the fixture 100 becomes too large during unloading is significantly minimized.

The conditions described above, i.e., the average potential of the electrodes 104A to 104D is set to negative, can be maintained for the entire duration of the exposure or for only a portion of the time before the unloading action of the multiplication mask MA. In some embodiments, the electrodes can be set to a certain state (e.g., configuration and/or specific potential) for only a portion of the exposure time. The electrodes do not necessarily need to be in the same configuration for the entire duration of the exposure. It may be necessary to set the electrodes to a balanced state (i.e., zero on average) to ensure that the multiplication mask becomes neutral.

Another embodiment is directed to preventing charging of the zoom mask MA during exposure. Again, this embodiment is about setting the electrostatic fixture 100 in a third mode so that the electrodes 104A to 104D have an average negative potential before the patterned device (zoom mask) MA is exposed (i.e., when the radiation beam B is incident on the patterned device MA, thereby providing the reflected patterned EUV radiation beam B' onto the substrate). However, in this embodiment, the potentials of the electrodes 104A to 104D are set to provide a negative offset of the potential to a specific value. This specific value can be calibrated to a specific zoom mask MA and exposure conditions, such as EUV dose. This specific value can be measured from a previous exposure and then fed forward. For example, for one reticle, the specific value may be set so that it provides a potential of -2V on the reticle and for another reticle MA, it may be -10V. Setting the reticle MA to the calibrated value (i.e., -2V) may mean that throughout the exposure, the potential of the reticle MA will not increase or decrease significantly overall because the transfer of charge caused by electrons and ions will be balanced. Therefore, at the end of the exposure, the reticle MA will have the same or similar charge as the previous exposure (e.g., -2V). In other embodiments, the specific value may be set so that it provides a potential on the reticle in the range of 0V to -20V.

The specific values of the negative potentials of the electrodes 104A to 104D can be selected so that after exposure, the reticle MA is substantially uncharged, i.e., at substantially zero charge. This means that during unloading (i.e., when the reticle MA is moved away from the jig 100), the potential difference between the second surface 124 of the reticle MA and the clamping surface 102 of the jig 100 does not increase significantly, as seen when the reticle MA is charged after exposure. The near-zero residual charge of the reticle MA while it is still close to the fixture 100, or even still physically connected to the fixture 100, significantly minimizes the risk of damage to the reticle MA due to discharge when the gap between the reticle MA and the fixture 100 becomes too large during unloading. In other embodiments, specific values may be selected so that the potential on the reticle MA matches the potential on the fixture 100, so that the potential difference between the second surface 124 of the reticle MA and the clamping surface 102 of the fixture 100 will not increase relatively.

The conditions described above, i.e., the average potential of the electrodes 104A to 104D is set to a specific negative value, can be maintained during the entire duration of the exposure or only during a portion of the time before the unloading action of the multiplication mask MA.

It will be appreciated that embodiments can be implemented by changing the software process without changing the hardware. This means that they can be implemented relatively quickly on the lithography equipment LA in the field and with little impact on production. Furthermore, embodiments can be reversible and flexible. They can be used as a temporary mitigation strategy (i.e. switched on and off or tuned when needed).

Since the embodiments may not require additional hardware, they may save commodity costs compared to other methods of implementing grounding of the zoom mask (e.g., during unloading). The embodiments may be directly applied to all EUV lithography equipment LA and may result in improved reliability and availability of the lithography equipment LA. In addition, the embodiments may be implemented by yield-neutral zoom mask grounding. The embodiments may result in higher yields.

FIG. 5 shows an embodiment of an electrostatic clamp 200 in which the polarities of four electrodes 204A to 204D are identified. The components of the electrostatic clamp 200 are similar to the components of the electrostatic clamp 100 of the previous embodiment and similar components will be provided with similar numbers increased by 100.

In the embodiment of FIG. 5 , electrodes 204A to 204D are identical to electrodes 104A to 104D of FIG. 4 a . Therefore, the capacitively induced potential on the multiplication mask MA (particularly on the second surface 224) remains constant (i.e., substantially 0V in this embodiment). However, this is only an example, and electrodes 204A to 204D may have different polarities and magnitudes, such as those shown in the previous embodiments. In any case, electrodes 204A to 204D provide clamping of the patterned device (multiplication mask) MA.

In the embodiment of FIG. 5 , there is an additional (or fifth) electrode 204E. The additional electrode 204E does not participate in clamping the zoom mask MA. The additional electrode 204E is located in the same plane as the electrodes 204A to 204D. The additional electrode 204E is located in a different plane than the zoom mask MA. In this embodiment, the additional electrode 204E is above the zoom mask MA, as shown in FIG. 5 .

The further electrode 204E is positioned at least partially around a (virtual) volume 230, which extends from the second surface 224 (back side) of the zoom mask MA in the direction of the electrostatic fixture 200 (i.e., the z direction). In other words, the further electrode 204E is positioned around the space above the second surface 224 of the zoom mask MA. The second surface 224 can be referred to as the surface of the zoom mask MA adjacent to the electrostatic fixture 200.

Volume 230 is shown in dashed lines extending from edge (or end) 228 of the abbreviated mask MA and the opposite end of the abbreviated mask MA. It should be understood that the right hand side of FIG. 5 does not show the entire abbreviated mask MA and that volume 230 can be considered to extend to the edge of the abbreviated mask MA on both sides. In this embodiment, edge 228 is closest to the EUV radiation beam B and therefore closest to the EUV induced plasma.

FIG. 6 shows the further electrode 204E and the patterned device MA from above (i.e. in plan view) - the electrostatic fixture 200 and the middle part of the electrodes 204A to 204D are not shown for clarity. The further electrode 204E is shown to extend all the way (i.e. completely) around the volume 230. The further electrode 204E can be applied to the dielectric of the electrostatic fixture 200. In practice, the area around the zoom mask MA is coated with the electrode 204E. The further electrode 204E can be a thin metal coating.

The other electrode 204E can be made of any suitable conductive material. For example, a material that is compatible with plasma and does not provide any problems. As an example, chromium nitride can be used as the material for the other electrode 204E.

The reticle collects electrical charge. Unloading a charged reticle causes the voltage in the reticle to increase. This can cause discharge and generate particles or damage.

The voltage on the further electrode 204E can be controlled. For example, in this embodiment, the potential on the further electrode 204E is set to negative. This sets the electric field around the zoom mask MA. This means that the electrons (i.e. free charges) generated by the mechanism can be repelled away from the second surface 224 of the zoom mask MA. This means that the number of electrons reaching the zoom mask MA is reduced. Therefore, the zoom mask can be prevented or at least reduced from being charged. This can avoid electrical collapse (e.g. during zoom mask unloading) resulting in indirect damage to the zoom mask surface. The magnitude of the potential of the further electrode 204E may not be comparable to that of the electrodes 204A to 204D, for example it may be much smaller.

It will be appreciated that in other embodiments, the further electrode 204E may be set positive. This sets the electric field around the zoom mask MA. This means that the positive ions (i.e. free charges) generated by the mechanism may be repelled away from the second surface 224 of the zoom mask MA. This means that the number of positive ions reaching the zoom mask MA will be reduced. Thus, the zoom mask charging will be prevented or at least reduced. This avoids electrical collapse (e.g. during zoom mask unloading) leading to indirect zoom mask surface damage.

More generally, the apparatus may be configured such that the further electrode 204E is arranged such that the flux of free charges generated by the mechanism to the second surface 224 is reduced. This flux of free charges may be considered to be reduced compared to when no electrode is present around the zoom mask or when the further electrode has a potential of 0 volts.

It will be appreciated that any size of the additional electrode 204E will provide some benefit. However, the larger the electrode (e.g., in the y-direction), the better it will repel charged particles, since a larger electrode will produce a larger electric field.

It will be appreciated that any negative (or positive) voltage set at the other electrode 204E will provide some benefit. However, the greater the voltage, the better the repulsion of charged particles, since a greater voltage produces a greater electric field. For example, the voltage may be 10 or 20 or 50 volts.

The surface of the further electrode 204E may be flat. However, in other embodiments, the surface may not be flat. For example, in an embodiment, the further electrode 204E may be rounded in the area corresponding to the corner of the zoom mask MA. This may increase the electric field. More generally, at least one or more edges of the further electrode 204E (i.e., the edges of the surface adjacent to the zoom mask MA) may be rounded.

In an embodiment, the further electrode 204E may be in electrical contact with the zoom mask MA (e.g., the second surface 224 of the zoom mask MA). This may allow direct control of the potential of the second surface 224 of the zoom mask MA. This may allow for greater repulsion of charged particles (e.g., electrons). The electrical contact may be made via one or more nodules. The nodules or nodules may be located within the volume 230.

In some embodiments, an electrical conductor (e.g., an existing ground conductor) may be used as the additional electrode 204E. In this case, an electrical supply may be connected to the ground conductor and a voltage may be provided to the ground conductor.

The potential of the electrode 204E can be set during at least a portion or all of the time when the mechanism generates free charge (e.g., during the exposure of the zoom mask MA). The potential of the electrode 204E can be set during a period of time before the zoom mask MA is moved from being clamped by the electrostatic clamp to being separated from the electrostatic clamp (e.g., just before releasing the zoom mask MA).

FIG. 6a shows another embodiment of the electrostatic fixture 200. This embodiment is the same as the embodiment of FIG. 5, except that the other electrode 204E is located on the other side of the clamping surface 202 and includes a plurality of walls. That is, the walls can be considered to be the sidewall electrode 204F extending upward (i.e., in the z direction) from the other electrode 204E to partially surround the electrostatic fixture 200, and the wall electrode 204G extending downward (i.e., in the direction opposite to the sidewall electrode 204F) from the other electrode 204E to partially surround the zoom mask MA. The walls can be metal plates. It should be understood that in some embodiments, both the sidewall electrode 204F and the wall electrode 204G need not exist. In addition, in some embodiments, one or both of the sidewall electrode 204F and the wall electrode 204G may be included in the electrode 204E or replace the other electrode 204E. In other embodiments, the other electrode 204E may also be located in the position shown in FIG. 5, and the sidewall electrode 204F and/or the wall electrode 204G may be located in the position shown in FIG. 6a.

In some embodiments, the further electrode 204E may also be set to a voltage that will deplete the free charges in the volume around MA. This may have the advantage of preventing the free charges from reaching (and charging) the multiplication mask MA. This may only be possible if the further electrode 204E is not coated with an isolation surface. For example, this may be possible if the coating has sidewall electrodes 204F and wall electrodes 204G as in FIG. 6a.

FIG. 7 shows another embodiment of the electrostatic chuck 200. This embodiment is the same as the embodiment of FIG. 6, except that there is a space (gap) 232 between the volume 230 and the other electrode 204E. That is, the other electrode does not need to be exactly around the volume 230.

FIG8 shows another embodiment of the electrostatic fixture 200. This embodiment is the same as the embodiment of FIG6, except that the further electrode 204E is only located on one side of the multiplication mask MA. Therefore, the further electrode 204E can be considered to at least partially surround the volume 230.

In this embodiment, the further electrode 204E is positioned adjacent to the edge 228 that is closest to the EUV radiation beam B and therefore closest to the EUV induced plasma. This side corresponds to the main direction of the charged particles, so it may be preferred to have the further electrode 204E on this side than on only one of the other sides. It will be appreciated that in other embodiments, the further electrode 204E may extend less or more in the x-direction. It will be appreciated that in other embodiments, the further electrode 204E may be on a different side than the edge 228.

FIG. 9 shows another embodiment of the electrostatic clamp 200. This embodiment is the same as the embodiment of FIG. 6 , except that there are four further electrodes 204E. That is, the further electrodes 204E are located on each side of the multiplication mask MA. In this embodiment, there are gaps between the further electrodes 204E. Therefore, the four further electrodes 204E can be considered to at least partially surround the volume 230. In other embodiments, in the case where there are no or substantially no gaps between the further electrodes 204E, the plurality of electrodes can be considered to completely surround the volume 230. It should be understood that in embodiments, there may be more or fewer than four further electrodes, such as 2, 3, 5, or 6, etc. For example, if there are two further electrodes, they may be located on two different sides, such as adjacent or opposite sides, or they may be located on the same side.

In an embodiment, the further electrodes 204E may be operated independently or in pairs or in any other group configuration. For example, one of the further electrodes 204E may be positively charged, another of the further electrodes 204E may be negatively charged and another further electrode 204E may be configured to reduce the flux of free charges generated by the mechanism to the second surface 224.

Referring to FIG. 4 c, another embodiment is now described. In the embodiment of FIG. 4 c, the average potential of all electrodes 104A to 104D is substantially 0V. More specifically, electrodes 104A and 104B have a positive potential (+) and electrodes 104C and 104D have a negative potential (-), wherein the magnitude of the potential of each of the electrodes 104A to 104D is substantially the same. It should be understood that the arrangement of electrodes 104A to 104D in FIG. 4 c is merely an example and other arrangements may be used, such as in FIG. 2 a, FIG. 3 a, or FIG. 4 a. It will be appreciated that there may be embodiments in which the or each potential of the electrode or each of the plurality of electrodes is not set so as to increase the flux of free charge generated by the mechanism to the surface of a component adjacent to the electrostatic fixture.

In the embodiment of FIG. 4c, the zoom mask (patterned device) MA is electrostatically clamped by two pairs of electrodes 104A to 104D, wherein the conductive second surface 124 (back surface) of the zoom mask MA is used as the opposing electrode. The capacitance of each electrode 104A to 104D in a pair is approximately equal. As a result, the potential of the second surface 124 remains close to ground. Therefore, the capacitively induced potential on the zoom mask MA (especially on the second surface 124) remains unchanged.

1/d)且因此增加了電位V=Q/C，其中Q為倍縮光罩上之電荷。倍縮光罩後側或前面電荷保持恆定直至發生放電，從而有可能導致缺陷度及/或護膜斷裂。 As mentioned previously, charging of the front and back of the reticle can lead to defectivity. Specifically, during the release period, the distance d between the back of the reticle and the electrode increases. This reduces the total electrode-reticle capacitance C (

1/d) and thus increases the potential V=Q/C, where Q is the charge on the zoom mask. The charge on the back or front of the zoom mask remains constant until discharge occurs, which may lead to defects and/or film cracking.

One way the reticle is charged is due to the EUV-induced plasma. In the most likely scenario, high-energy (photo) electrons arrive at the back of the reticle and induce negative charge. During this process, the potential at the back of the reticle will become increasingly negative. When the back of the reticle starts at ground potential, charging is a rapid "uphill" process, requiring more and more high-energy electrons to overcome the increasing negative potential. The process can be saturated at approximately -10V.

As mentioned, since the capacitance of each of the electrodes 104A-104D in a pair is substantially equal, the potential of the second surface 124 remains close to ground. However, even if the average potential of all electrodes 104A-104D is substantially 0V, there may be capacitively induced potentials on the second surface 124 of the zoom mask MA. This may be due to a small imbalance in the capacitance of the electrostatic fixture 100 (more specifically, the capacitance of the individual electrodes 104A-104D). This imbalance may induce a positive (or negative) potential in the second surface 124 of the zoom mask MA.

In some examples, the clamping surface 102 of the electrostatic clamp 100 is almost completely flat, but the control of the zoom mask-electrode spacing is not precise. That is, the spacing between the electrodes 104A to 104D and the second surface 124 of the zoom mask MA may be slightly different for some or all of the electrodes 104A to 104D. This may be, for example, because the clamping surface 102 is tilted relative to the second surface 124 of the zoom mask MA. As a result, each clamp 100 will have a slightly different electrode capacitance. In addition, the electrode capacitance will likely vary depending on the zoom mask MA clamped.

Positive residual potential on the back side of the reticle can accelerate (negative) reticle back side charging and can cause larger potential (and discharge) during unloading. Furthermore, lack of control over reticle back side charging may make controlled unbalanced clamping to induce negative reticle back side potential (no charge) unfeasible.

There is a problem in achieving reliable control of the reticle backside potential at least below about 10V. This level of control is needed to prevent discharge during reticle unloading. The problem is not the control of the (high) voltage applied to the reticle fixture, but the uncertainty of the fixture electrode-reticle backside capacitance.

FIG. 10 shows a schematic circuit diagram of the back side (second surface 124) of the multiplication mask (patterned device) MA, electrodes 104A to 104D, and a high voltage supply. The capacitance of each of the electrodes 104A to 104D (combined with the back side of the multiplication mask) is depicted as C1 to C4, respectively. Each of the electrodes 104A to 104D is powered by a high voltage supply, which has a voltage depicted as V1 to V4, respectively.

A plurality of charge measuring devices 300A to 300D are provided, one charge measuring device for each electrode 104A to 104D. The charge measuring devices 300A to 300D measure the charge from the voltage supply to the electrodes 104A to 104D.

It should be understood that this is only one embodiment and in other embodiments, there may be different electronic device arrangements. For example, there may be only two electrodes (e.g., electrodes 104A and 104C) or there may be a single charge measuring device configured to measure the charge of each of the electrodes.

The charge measurement devices 300A to 300D are used to measure the fixture-reduction mask capacitance. This measurement is relatively non-trivial because the second surface 124 of the reduction mask MA has no contacts, i.e., it is floating.

At the level of high voltage power amplifiers, it is not possible to directly measure the capacitance of individual electrodes 104A to 104D. For example, when V1 is changed by step dV1, the change in charge to electrode 104A (i.e., dQ1) is: dQ1=dV1*(1/C1+1/(C2+C3+C4)) ^-1 .

That is, the series capacitance of C1 and C2+C3+C4 is measured. However, in the case of having charge measuring devices 300A to 300D (one charge measuring device for each high voltage source of the fixture 100), the capacitance or the ratio of the capacitances can be determined.

When the potential of, for example, electrode 104A changes by an amount dV1, the potential of the second surface 124 of the zoom mask MA will change by a substantially unknown amount dVb. This in turn induces a change in the charge to electrodes 104A to 104D: dQ1=C1*(dVb-dV1) dQ2=C2*dVb dQ3=C3*dVb dQ4=C4*dVb(dQ1+dQ2+dQ3+dQ4)=0 (since no net charge reaches the second surface 124 of the zoom mask MA).

The measured charge is given by the following equation: _Qn = ( _Vn - _Vb ). _Cn

Wherein n=1…4, _Cn is the unknown capacitance of electrodes 104A to 104D, _Qn is the charge measured by charge measuring devices 300A to 300D, _Vb is the potential of the second surface (back surface) 124 of the zoom mask MA, and _Vn is the potential applied to electrodes 104A to 104D.

In an embodiment, the multiplication mask MA is clamped and flattened relative to the nodule by applying a first set of sufficiently high potentials V _n,1 , e.g., V _n,1 =(-1) ⁿ Φ _1. This results in four equations and five unknowns (C _1-4 and V _b,1 ). Next, the multiplication mask MA potential is changed, i.e., the potentials of the electrodes 104A to 104D are changed, e.g., to V _n,2 =(-1) ⁿ Φ ₂ . This results in eight equations and six unknowns (C _1-4 and V _b,1 , V _b,2 ). Having more equations than unknowns allows the equations to be solved for C _n , V _b,1 , and V _b,2 . Therefore, the capacitance of the electrodes 104A to 104D, the potential (V _b,1 ) of the second surface 124 having the first set of high potentials V _n, 1, and the potential (V b _,2 ) of the second surface 124 having the second set of high potentials V _n,2 are determined.

Now that the potential of the second surface V _b,2 has been determined, the potential of electrodes 104A to 104D can be adjusted to achieve the desired back surface potential (V _b ) using the now known C _n using this equation: V _b = sum(V _n · C _n )/sum(C _n )

For example, when zero back surface potential is required, V _n = Φ ₂ ． C ₁ /C _n can be selected.

It is preferred that the potential of one or more electrodes 104A to 104D is set so that the potential of the second surface 124 is negative before or at least relatively soon after the mechanism for generating free charges is turned on (e.g., the zoom mask MA is exposed to EUV radiation). This potential can be maintained for the entire time that the mechanism generates free charges. This can minimize the number of negative charges attracted to the second surface 124. However, in an embodiment, the potential can be set so that the potential of the second surface 124 is negative during part of the EUV exposure time and/or in the time period before the zoom mask MA is moved from being clamped by the electrostatic fixture 100 to being separated from the electrostatic fixture 100.

Preferably, the potential of one or more electrodes 104A to 104D is set so that the potential of the second surface 124 is substantially zero before the time when the mechanism generates free charge (e.g., before exposure of the multiplication mask MA). This can minimize the number of negative charges attracted to the second surface 124. This may be because if the potential of the electrodes is only set some time after the start of EUV exposure, the second surface 124 may already have a negative charge due to fast moving negative electrons, which may then not be able to reduce sufficiently before the clamp 100 is released.

It will be appreciated that the described measurement and potential setting processes can be used in conjunction with, for example, using EUV-induced plasma to remove charge from the backside of a reticle. It will be appreciated that these measurement and potential setting processes can be used in conjunction with the above described methods of increasing the flux of free charge generated by an EUV source.

Variations on the above scheme are possible. For example, the first potential step from zero to Φ ₁ will actually be larger than the second step from Φ ₁ to Φ ₂ , where |Φ ₁ - Φ ₂ | is typically less than 10% of |Φ ₁ |. As a result, the charge measurement devices 300A to 300D may need to have a high dynamic range. It may be beneficial to first clamp the zoom mask MA at a high potential and then vary the fixture potential to account for the change in charge: ΔQ _n =(ΔV _n -ΔV _b ). C _n

In a similar manner, C _n and therefore the potential of the second surface 124 of the zoom mask MA can be determined by applying two sets of potential steps ΔV _n,1 and ΔV _n,2 having similar magnitudes.

In an example, the electrode arrangement of the fixture 100 may be considered similar to the arrangement shown, for example, in FIG. 2a. It should be understood that this is only an example and other arrangements of electrodes may be used.

In addition to being able to maintain the potential of the second surface 124 of the doubling mask MA at substantially zero volts (i.e., at ground), the potential of the second surface 124 can also be maintained at a (approximately) specific negative (or positive) predetermined value. That is, the potential of the second surface 124 of the doubling mask MA can be maintained at an approximately controlled potential. In other words, the potential of one or more of the electrodes 104A to 104D can be set so that the potential of the second surface 124 is substantially a predetermined value. It is preferable to set the potential of one or more electrodes 104A to 104D so that the potential of the second surface 124 is negative, so that high-energy (photo) electrons are repelled from the second surface 124 of the doubling mask MA (or at least not attracted to the second surface 124 of the doubling mask MA).

Using the charge or charges measured by one or more charge measuring devices 300A to 300D and the capacitances C1 to C4 of the electrodes 104A to 104D, the potential of the second surface 124 of the zoom mask MA can be determined. Determining the potential can be considered as, for example, measuring, calculating or setting the potential of the second surface 124.

The capacitance of electrodes 104A-104B may vary only by a certain percentage, such as +/-10%. For a nominal fixture capacitance, an unbalanced electrode 104A of -100V may result in a -25V backside potential. Then, correcting for the measured capacitance of the electrodes, a potential of -25V +/-~10% may be applied to the second surface 124, for example to mitigate electron charging.

Since capacitance may only vary +/-~10%, simply aiming for a >-10V back potential (using the nominal fixture capacitance) may be sufficient to ensure that a negative potential exists on the second surface 124. In the above example, a -25V back potential may be aimed for to ensure that there is some margin to ensure that the second surface 124 will definitely eventually become negative to mitigate electron charging. More generally, the potential of at least one of the electrodes 104A-104D may be set based on the variance of the capacitance of one or more of the electrodes 104A-104D.

In other embodiments, the electrode may be changed to have a more positive value (e.g. +100V), which may result in, for example, a +25V back surface potential. This may be applicable in situations where it is desired to reduce positive ion charging of the second surface 124.

In addition to determining the capacitances C1 to C4 as described above, other methods are possible to determine the capacitances C1 to C4 of individual electrodes 104A to 104D. This can be done by applying voltage steps to different electrodes 104A to 104D and then measuring the charge transfer. In other words, the potential of the electrodes 104A to 104D is changed by a predetermined amount in a stepwise manner, and after each potential change, the charge measurement devices 300A to 300D are used to measure the charge from the voltage supply to the electrodes 104A to 104D, respectively.

This results in an (over)constrained set of equations that can be solved for the individual capacitances C1 to C4. The four voltages V1, V2, V3, V4 can be varied stepwise and together with the measured charge from each of the charge measurement devices 300A to 300D, there is sufficient information to determine C1 to C4 individually. In this embodiment, the charge to each electrode 104A to 104D can be measured. However, it should be appreciated that this is only an example and variations on a wide range of measurements are possible.

As an example, at least two voltage steps may be applied, such as dV1 and dV2. This then generates 8 equations and 6 unknowns (C _1-4 , dV _b1, dV _b2 ). This set may be solved. The absolute values of C1 to C4 may then be obtained. This allows the second surface 124 of the zoom mask MA to be set to 0V by observing, for example, V4/V3=-C3/C4 and V2/V1=-C1/C2. Thus, in an embodiment, the potential of the electrodes 104A to 104D may be based on the ratio of the capacitances of the electrodes 104A to 104D. Alternatively, instead of setting the second surface 124 of the zoom mask MA to 0V, any arbitrary potential may be set.

Alternatively, in other embodiments, two electrodes may be left floating and a single charge measurement may be used to determine the series capacitance of the other two electrodes. For example, the capacitance of C1 to C2 may be measured in series ( _C12 ) and then _C13 , _C14 , _C23 , _C24 , and _C34 may be similarly measured. Using 6 unique combinations again provides an over-constrained set of equations that may be used to derive the individual capacitances C1 to C4. It will be appreciated that many variations are possible and may be co-optimized with hardware development.

The above derivation neglects stray capacitances, such as cable-to-ground capacitances of 50 to 100 pF/m. In a practical implementation, these capacitances should be included and corrected for. This is possible by, for example, applying a potential to the zoom mask fixture without the zoom mask. In that case, the fixture-to-zoom mask capacitance is effectively zero and the stray capacitance can be measured.

Although the above is generally related to one or more charge measuring devices 300A-300D measuring the charge Q to the electrodes 104A-104D, it should be understood that in other embodiments, other measuring devices may be used. For example, in embodiments, one or more current measuring devices for measuring the current to the electrodes may be used instead of or in addition to the charge measuring devices 300A-300D. In embodiments, an oscillating electrode potential _Vn = _Vn0 + _Va *sin(Ω*t) may be applied. The AC portion of the current entering the electrostatic fixture may then be measured. Thus, instead of measuring Q or ΔQ, dQ/dt (=I) may then be measured.

It will be appreciated that the use of the current measuring device or devices to determine the potential of the second surface 124 of the zoom mask MA (by calculating the capacitance of one or more electrodes 104A to 104D using the measured current to one or more of the electrodes 104A to 104D) can function in a manner similar to the use of the charge measuring devices 300A to 300D. As mentioned, in the above embodiments regarding charge measurement, Q versus V or dQ versus dV is measured. However, dQ/dt=I versus dV/dt may also be measured. The equivalent will be appreciated, since: Q=C*V, dQ=C*dV, dQ/dt=I=C*dV/dt.

It will be appreciated that calculations etc. may be performed in the device and/or in a separate system (e.g., a computer device).

Although specific reference may be made herein to the use of lithography equipment in IC manufacturing, it should be understood that the lithography equipment described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guide and detection patterns for magnetic resonance memory, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

Although embodiments of the invention may be specifically referenced herein in the context of lithography equipment, embodiments of the invention may be used in other equipment. Embodiments of the invention may form part of a mask inspection equipment, a metrology equipment, or any equipment that measures or processes objects such as wafers (or other substrates) or masks (or other patterned devices). Such equipment may generally be referred to as a lithography tool. The lithography tool may use vacuum conditions or ambient (non-vacuum) conditions.

Although the foregoing may specifically refer to the use of embodiments of the present invention in the context of optical lithography, it should be understood that the present invention may be used in other applications (such as imprint lithography) and is not limited to optical lithography where the context permits.

Where the context allows, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium that can be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form that can be read by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; propagation signals in electrical, optical, acoustic, or other forms (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Additionally, firmware, software, routines, instructions, etc. may be described herein as performing certain actions. However, it should be understood that such descriptions are for convenience only and that such actions in fact result from a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc. and causing an actuator or other device to interact with the physical world when performing such operations.

Although specific embodiments of the present invention have been described above, it should be understood that the present invention may be practiced in other ways than those described. The above description is intended to be illustrative and not restrictive. Therefore, it will be apparent to those skilled in the art that modifications may be made to the present invention as described without departing from the scope of the claims set forth below.

100: Electrostatic clamp

102: generally flat clamping surface

104A: Electrode/Edge Electrode

104B: Electrode

104C: Electrode

104D: Electrode

122: First plane surface/front surface

124: Second plane surface/rear surface

126: Base plate

128: Reduction mask edge

MA: Patterned device/reduction mask

MT: Support structure

Claims (62)

An electrostatic device, comprising: an electrostatic clamp for clamping a component; and a mechanism for generating free charge adjacent to the electrostatic clamp: wherein the electrostatic clamp comprises an electrode or a plurality of electrodes, wherein the device is configured to: operate in a first mode, in which the electrode or each of the plurality of electrodes is set at an electric potential such that a clamping electric field is generated between the electrostatic clamp and the component to clamp the component, operating in a second mode in which the or each potential of the electrode or each of the plurality of electrodes is set such that the component is unclamped, and operating in a third mode in which the or each potential of the electrode or each of the plurality of electrodes is set such that the flux of free charge generated by the mechanism to a surface of the component adjacent the electrostatic fixture is increased compared to operating in the first or second mode. The device of claim 1, wherein the electrostatic fixture includes the plurality of electrodes, and wherein in the third mode, the device is configured so that the potential of an edge electrode closest to an edge of the electrostatic fixture is set to positive. A device as claimed in claim 1 or 2, wherein in the third mode, the device is configured so that the potential of the electrode or each of the plurality of electrodes is set so that the potential of the electrode or the average potential of the plurality of electrodes is negative. The device of claim 2, wherein in the third mode, the device is configured so that the potentials of the plurality of electrodes are set so that the average potential of the plurality of electrodes is substantially 0V. The device of claim 1, wherein the electrostatic fixture includes the plurality of electrodes, and wherein in the third mode, the device is configured so that the potential of an edge electrode closest to an edge of the electrostatic fixture is set to negative, and the potential of the remaining portion of the plurality of electrodes is set so that the average potential of the plurality of electrodes has a less negative value than the potential of the edge electrode. The apparatus of claim 3, wherein in the third mode, the apparatus is configured so that the potential of the electrode or each of the plurality of electrodes is set so that the surface of the component adjacent to the electrostatic fixture has a positive potential before the component is moved from being held by the electrostatic fixture to being spaced apart from the electrostatic fixture. The apparatus of claim 3, wherein in the third mode, the potential of the electrode or the average potential of the electrodes is set to a predetermined negative value so that during the period when the component is moved from being clamped by the electrostatic fixture to being separated from the electrostatic fixture, the surface of the component has a potential substantially the same as the potential of the electrode or the average potential of the electrodes. The apparatus of claim 7, wherein in the third mode, the potential of the electrode or the average potential of the electrodes is set to the predetermined negative value so that after the component is exposed, the component has substantially zero charge. The apparatus of claim 1 or 2, wherein in the third mode, the potential of the electrode or each of the plurality of electrodes is set within at least one of the following times: a period of time before the component is moved from being clamped by the electrostatic clamp to being separated from the electrostatic clamp; a portion or all of the time it takes for the component to be moved from being clamped by the electrostatic clamp to being separated from the electrostatic clamp; and a portion or all of the time it takes for the component to be moved from being separated from the electrostatic clamp to being clamped by the electrostatic clamp. An apparatus as claimed in claim 1 or 2, wherein in the third mode, the potential of the electrode or an average potential of one of the electrodes is set during at least a portion or all of the time that the mechanism generates free charge. The apparatus of claim 1 or 2, wherein the mechanism for generating free charge in proximity to the electrostatic fixture may include: a gas source; and an ionizing radiation source configured to ionize a gas provided by the gas source. The apparatus of claim 11, wherein the ionizing radiation source comprises at least one of an EUV source, a VUV source, a soft x-ray source, and a radioactive source. A device as claimed in claim 1 or 2, wherein the electrostatic fixture comprises a further electrode or a plurality of further electrodes, wherein the further electrode or the plurality of further electrodes are positioned at least partially around a volume extending from a surface of the component adjacent to the electrostatic fixture in the direction of the electrostatic fixture, wherein the device is configured so that the or each potential of the or each further electrode is set so that the flux of free charge generated by the mechanism to the surface of the component adjacent to the electrostatic fixture is reduced. The apparatus of claim 1 or 2, wherein the apparatus is configured to: measure charge or current from a voltage supply to the electrode or each of the plurality of electrodes using at least one charge or current measuring device; calculate capacitance of the electrode or each of the plurality of electrodes using the measured charge or current to the electrode or each of the plurality of electrodes; and determine the potential of a surface of the component adjacent to the electrostatic fixture using the calculated capacitance of the electrode or each of the plurality of electrodes. A lithography apparatus configured to project a pattern from a patterned device onto a substrate, wherein the lithography apparatus comprises an illumination system configured to modulate a radiation beam and an apparatus as claimed in any one of claims 1 to 14, wherein the illumination system is configured to project the radiation beam onto the patterned device, and wherein the patterned device comprises a component to be clamped, wherein the lithography apparatus comprises an apparatus as claimed in any one of claims 1 to 14. A method of operating an apparatus, the apparatus comprising: an electrostatic fixture; and a mechanism for generating free charge adjacent to the electrostatic fixture, the electrostatic fixture comprising an electrode or a plurality of electrodes, the method comprising: providing a component adjacent to the electrostatic fixture; controlling the mechanism for generating free charge to generate free charge adjacent to the electrostatic fixture, so that the apparatus operates in a first mode, in which the electrode or each of the plurality of electrodes is set at an electric potential such that in the electrostatic fixture, the free charge is generated adjacent to the electrostatic fixture. A clamping electric field is generated between the electrostatic chuck and the component to clamp the component, so that the device operates in a second mode, in which the potential of the electrode or each of the plurality of electrodes is set so that the component is released, and the device operates in a third mode, in which the potential of the electrode or each of the plurality of electrodes is set so that the flux of free charges to a surface of the component adjacent to the electrostatic chuck is increased compared to operation in the first or second mode. The method of claim 16, wherein the electrostatic fixture includes a plurality of electrodes, the method further comprising: in the third mode, setting the potential of an edge electrode closest to an edge of the electrostatic fixture to positive. The method of claim 17 further comprises: in the third mode, setting the potential of the electrode or each of the plurality of electrodes so that the potential of the electrode or the average potential of the plurality of electrodes is negative. The method of claim 17 further comprises: in the third mode, setting the potentials of the plurality of electrodes so that the average potential of the plurality of electrodes is substantially 0V. A method as claimed in any one of claims 16 to 19, wherein the electrostatic fixture comprises a further electrode or a plurality of further electrodes, the further electrode or the plurality of further electrodes being positioned at least partially around a volume, the volume extending from a surface of the component adjacent to the electrostatic fixture in the direction of the electrostatic fixture, the method further comprising: Setting the or each potential of the or each further electrode so that the flux of free charge to the surface of the component adjacent to the electrostatic fixture is reduced. The method of any one of claims 16 to 19, further comprising: using at least one charge or current measuring device to measure the charge or current from a voltage supply to the electrode or each of the plurality of electrodes; using the measured charge or current to the electrode or each of the plurality of electrodes to calculate the capacitance of the electrode or each of the plurality of electrodes; and using the calculated capacitance of the electrode or each of the plurality of electrodes to determine the potential of a surface of the component adjacent to the electrostatic fixture. A computer program comprising computer-readable instructions configured to cause a processor to perform a method as recited in any one of claims 16 to 21. A computer-readable medium carrying a computer program as claimed in claim 22. A computer device for operating a device, comprising: a memory storing processor-readable instructions; and a processor configured to read and execute instructions stored in the memory; wherein the processor-readable instructions include instructions configured to control the computer to perform a method as in any one of claims 16 to 21. An electrostatic device, comprising: an electrostatic fixture for clamping a component; and a mechanism for generating free charges adjacent to the electrostatic fixture: Wherein the electrostatic fixture comprises an electrode or electrodes, wherein the electrode or electrodes are positioned at least partially around a volume, the volume extending from a surface of the component adjacent to the electrostatic fixture in the direction of the electrostatic fixture, wherein the device is configured so that the or each potential of each of the electrode or electrodes is set so that the flux of free charges generated by the mechanism to the surface of the component adjacent to the electrostatic fixture is reduced. A device as claimed in claim 25, wherein the electrode or the plurality of electrodes are located on one side of the component. A device as claimed in claim 25 or 26, wherein the electrode or electrodes extend all the way around the volume. A device as claimed in claim 25 or 26, wherein the potential of the electrode or each of the plurality of electrodes is set to negative. A device as claimed in claim 25 or 26, wherein the potential of the electrode or each of the plurality of electrodes is set to positive. The apparatus of claim 25 or 26, wherein the electrode or each of the plurality of electrodes is in electrical contact with the surface of the component adjacent to the electrostatic fixture. A device as claimed in claim 25 or 26, wherein at least one or more edges of the surface of the electrode or each of the plurality of electrodes adjacent to the component are rounded. A device as claimed in claim 31, wherein the electrode or each of the plurality of electrodes is circular in the region corresponding to the corner of the component. The apparatus of claim 25 or 26, wherein the potential of the electrode or each of the plurality of electrodes is set during at least one of the following times: at least a portion or all of the time during which the mechanism generates free charge, and a period of time before the component is moved from being held by the electrostatic fixture to being separated from the electrostatic fixture. The apparatus of claim 25 or 26, wherein the mechanism for generating free charge in proximity to the electrostatic fixture comprises: a gas source; and an ionizing radiation source configured to ionize a gas provided by the gas source. The apparatus of claim 34, wherein the ionizing radiation source comprises at least one of an EUV source, a VUV source, a soft x-ray source, and a radioactive source. A lithography apparatus configured to project a pattern from a patterned device onto a substrate, wherein the lithography apparatus comprises an illumination system configured to modulate a radiation beam and an apparatus as claimed in any one of claims 25 to 35, wherein the illumination system is configured to project the radiation beam onto the patterned device, and wherein the patterned device comprises a component to be clamped, wherein the lithography apparatus comprises an apparatus as claimed in any one of claims 25 to 35. A method of operating an apparatus comprising: an electrostatic fixture; and a mechanism for generating free charge adjacent to the electrostatic fixture, the electrostatic fixture comprising an electrode or electrodes, the electrode or electrodes being positioned at least partially around a volume, the volume being adjacent to the electrostatic fixture in a direction of the electrostatic fixture. The method comprises: providing a component adjacent to the electrostatic fixture; controlling the mechanism for generating free charge to generate free charge adjacent to the electrostatic fixture, and setting the or each potential of the or each other electrode so that the flux of free charge to the surface of the component adjacent to the electrostatic fixture is reduced. The method of claim 37 further comprises setting the potential of the electrode or each of the plurality of electrodes to negative. The method of claim 37 further comprises setting the potential of the electrode or each of the plurality of electrodes to be positive. A method as claimed in any one of claims 37 to 39, further comprising controlling the potential of the surface of the component adjacent to the electrostatic fixture via an electrical connection between the electrode or each of the plurality of electrodes and the surface of the component adjacent to the electrostatic fixture. A computer program comprising computer-readable instructions configured to cause a processor to perform a method as recited in any one of claims 37 to 40. A computer-readable medium carrying a computer program as claimed in claim 41. A computer device for operating a device, comprising: a memory storing processor-readable instructions; and a processor configured to read and execute instructions stored in the memory; wherein the processor-readable instructions include instructions configured to control the computer to perform a method as in any one of claims 37 to 40. An electrostatic device, comprising: an electrostatic fixture for clamping a component; and a mechanism for generating free charge adjacent to the electrostatic fixture: wherein the electrostatic fixture includes an electrode or multiple electrodes, wherein the device is configured to: use at least one charge or current measuring device to measure the charge or current from a voltage supply to the electrode or each of the multiple electrodes; use the measured charge or current to the electrode or each of the multiple electrodes to calculate the capacitance of the electrode or each of the multiple electrodes; and use the calculated capacitance of the electrode or each of the multiple electrodes to determine the potential of a surface of the component adjacent to the electrostatic fixture. The apparatus of claim 44, wherein the apparatus is configured so that the potential of one or each of the plurality of electrodes is set so that the potential of a surface of the component adjacent to the electrostatic fixture is substantially a predetermined value. The apparatus of claim 44 or 45, wherein the predetermined value of the potential of the surface of the component adjacent to the electrostatic fixture is at least one of positive, negative, and substantially zero. A device as claimed in claim 44 or 45, wherein the device is configured to measure a ratio of the capacitances of the plurality of electrodes. The device of claim 47, wherein the device is configured to set the potential of at least one of the plurality of electrodes based on the ratio of the capacitances of the plurality of electrodes. A device as claimed in claim 44 or 45, wherein the device is configured to set the potential of at least one of the plurality of electrodes based on a variance of the capacitance of the electrode or each of the plurality of electrodes. The device of claim 44 or 45, wherein the device is configured to change the potential of the plurality of electrodes by a predetermined amount in a stepwise manner, and after each potential change, use the at least one charge or current measuring device to measure the charge or current from the voltage supply to the electrode or each of the plurality of electrodes for determining the individual capacitances of the plurality of electrodes. The apparatus of claim 44 or 45, wherein the potential of the electrode or each of the plurality of electrodes is set within at least one of the following times: before the mechanism generates free charge, at least a portion of the time, or all of the time; and before the component is moved from being clamped by the electrostatic fixture to being separated from the electrostatic fixture. The apparatus of claim 44 or 45, wherein the mechanism for generating free charge in proximity to the electrostatic fixture comprises: a gas source; and an ionizing radiation source configured to ionize a gas provided by the gas source. The apparatus of claim 52, wherein the ionizing radiation source comprises at least one of an EUV source, a VUV source, a soft x-ray source, and a radioactive source. A lithography apparatus configured to project a pattern from a patterned device onto a substrate, wherein the lithography apparatus comprises an illumination system configured to modulate a radiation beam and an apparatus as claimed in any one of claims 44 to 53, wherein the illumination system is configured to project the radiation beam onto the patterned device, and wherein the patterned device comprises a component to be clamped, wherein the lithography apparatus comprises an apparatus as claimed in any one of claims 44 to 53. A method of operating an apparatus comprising: an electrostatic fixture; and a mechanism for generating free charge adjacent to the electrostatic fixture, the electrostatic fixture comprising an electrode or a plurality of electrodes, the method comprising: providing a component adjacent to the electrostatic fixture; controlling the mechanism for generating free charge to generate free charge adjacent to the electrostatic fixture, using at least one charge or current flow The measuring device measures a charge or current from a voltage supply to the electrode or each of the plurality of electrodes, calculates a capacitance of the electrode or each of the plurality of electrodes using the measured charge or current to the electrode or each of the plurality of electrodes, and determines a potential of a surface of the component adjacent to the electrostatic fixture using the calculated capacitance of the electrode or each of the plurality of electrodes. The method of claim 55 further includes setting the potential of one or each of the plurality of electrodes so that the potential of a surface of the component adjacent to the electrostatic fixture is substantially a predetermined value. The method of claim 55 or 56 further includes setting the potential of the one or each of the plurality of electrodes so that the predetermined value of the potential of the surface of the component adjacent to the electrostatic fixture is at least one of positive, negative and substantially zero. The method of claim 55 or 56 further comprises setting the potential of at least one of the plurality of electrodes based on the ratio of the capacitances of the plurality of electrodes. The method of claim 55 or 56 further comprises setting the potential of at least one of the plurality of electrodes based on the variance of the capacitance of the electrode or each of the plurality of electrodes. A computer program comprising computer-readable instructions configured to cause a processor to perform a method as recited in any one of claims 55 to 59. A computer-readable medium carrying a computer program as claimed in claim 60. A computer device for operating a device, comprising: a memory storing processor-readable instructions; and a processor configured to read and execute instructions stored in the memory; wherein the processor-readable instructions include instructions configured to control the computer to perform a method as in any one of claims 55 to 59.