TWI880958B - A lithography apparatus and a method of detecting a radiation beam - Google Patents

Abstract

A substrate table configured to hold a substrate, comprising: a plurality of sensor elements configured to detect a radiation beam from a projection system, the radiation beam forming an illuminated region having an elongate shape at substrate level, the elongate shape having long edges and short edges and defining a longitudinal direction and a transverse direction perpendicular to the longitudinal direction, the sensor elements arranged along the longitudinal direction, wherein the plurality of the sensor elements are arranged at different distances in the transverse direction from one of the long edges of the elongate shape

Description

Lithography equipment and method for detecting radiation beam

The present invention relates to a lithography device and a method for detecting a radiation beam in a lithography device.

A lithographic apparatus is a machine that applies a desired pattern to a substrate, usually to a target portion of the substrate. Lithographic apparatus may be used, for example, in the manufacture of integrated circuits (ICs). In that case, a patterning device (which is alternatively referred to as a mask or reticle) may be used to produce the circuit pattern to be formed on individual layers of the IC. This pattern may be transferred to a target portion (e.g., a portion containing a die, a die, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is usually performed by imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. Generally, a single substrate will contain a network of adjacent target portions that are patterned continuously.

Lithography is widely recognized as one of the key steps in the fabrication of ICs and other devices and/or structures. However, as the size of features fabricated using lithography becomes smaller and smaller, lithography is becoming a more decisive factor in enabling the fabrication of small ICs or other devices and/or structures.

Theoretical estimates of the pattern printing limit can be given by the Rayleigh resolution criterion, as shown in equation (1):

where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection system used to print the pattern, _k1 is a process-dependent adjustment factor (also called the Rayleigh constant), and CD is the feature size (or critical dimension) of the printed feature. From equation (1), it can be seen that a reduction in the minimum printable size of a feature can be obtained in three ways: by shortening the exposure wavelength λ, by increasing the numerical aperture NA, or by reducing the value of _k1 .

In order to shorten the exposure wavelength and thus reduce the minimum printable size, it has been proposed to use a deep ultraviolet (EUV) radiation source or an extreme ultraviolet (EUV) radiation source. EUV radiation is electromagnetic radiation with a wavelength in the range of 10nm to 20nm, for example in the range of 13nm to 14nm. It has further been proposed to use EUV radiation with a wavelength less than 10nm, for example in the range of 5nm to 10nm, such as 6.7nm or 6.8nm. This radiation is called extreme ultraviolet radiation or soft x-ray radiation. Possible sources include, for example, laser-generated plasma sources, discharge plasma sources, or sources based on synchrotron radiation provided by electron storage rings.

EUV radiation may be generated using a plasma. A radiation system for generating EUV radiation may include a laser for exciting a fuel to provide a plasma, and a source collector module for containing the plasma. The plasma may be generated, for example, by directing a laser beam at a fuel, such as particles of a suitable material (e.g., tin), or a stream of a suitable gas or vapor (e.g., Xe gas or Li vapor). The resulting plasma emits output radiation, such as EUV radiation, which is collected using a radiation collector. The radiation collector may be a mirrored normal incidence radiation collector that receives the radiation and focuses the radiation into a beam. The source collector module may include an enclosure or chamber configured to provide a vacuum environment to support the plasma. This radiation system is often called a laser-produced plasma (LPP) source.

A sensor may be provided for detecting a property of a radiation beam. This radiation beam may be a patterned radiation beam, i.e. a radiation beam on which a patterning device has imparted a pattern. For example, the deviation of the measured radiation beam from a nominal (e.g. ideal) radiation beam may be measured. This may allow for the possibility of compensating for the deviation.

In order to measure how the patterned radiation beam changes across the illuminated area at the substrate level, it may be necessary to perform multiple measurements. Performing multiple measurements increases the measurement time.

It is desirable to provide a substrate apparatus and a method for detecting a radiation beam that allows the total measurement time to be reduced.

According to one aspect of the present invention, a lithography apparatus is provided, comprising: a substrate stage configured to hold a substrate; and a projection system configured to project a radiation beam to form an illuminated area having an elongated shape at the substrate level, the elongated shape having long edges and short edges and defining a longitudinal direction and a transverse direction perpendicular to the longitudinal direction; wherein the substrate stage comprises a plurality of sensor elements configured to detect the radiation beam, the sensor elements being arranged along the longitudinal direction, wherein the plurality of the sensor elements are arranged at different distances from one of the long edges of the elongated shape in the transverse direction.

According to one aspect of the present invention, a method for detecting a radiation beam in a lithography apparatus is provided, the method comprising: providing a projected radiation beam; projecting the projected radiation beam to form an illuminated area having an elongated shape at a substrate level, the elongated shape having long edges and short edges and defining a longitudinal direction and a transverse direction perpendicular to the longitudinal direction; using a plurality of sensor elements at the substrate level to detect the radiation beam, the sensor elements being arranged along the longitudinal direction, wherein the plurality of sensor elements are arranged at different distances from one of the long edges of the elongated shape in the transverse direction.

10: Radiation sensor

11: Lighting area

12: Long edge

13: Short edge

14: Centerline

15: Longitudinal direction

16: Horizontal direction

17: Sensor components

18: Downstream arrow/intensity flat line area

19: Central area

21: Radiation beam

22: Faceted field mirror device

24: Faceted pupil mirror device

26: Patterned radiation beam

27: Compare dots

28: Reflective element

30: Reflective element

100: Lithography equipment

210: EUV radiation emitting plasma/ultra-hot plasma/thermal plasma/highly ionized plasma

211: Source chamber

212: Collector chamber

220: Enclosed structure

221: Open your mouth

230: Select gas barrier/contaminant trap/contaminant trap/contaminant barrier

240: Grating spectral filter

251: Upstream radiation collector side

252: Downstream radiation collector side

253: Grazing incidence reflector

254: Grazing incidence reflector

255: Grazing incidence reflector

B:Radiation beam

C: Target section

CO: Radiation collector/collector optics

IF: Virtual origin/middle focus

IL: lighting system/illuminator/lighting optical unit

LA: Laser

M1: Mask alignment mark

M2: Mask alignment mark

MA: Patterned device

MT: Support structure

O: optical axis

P1: Substrate alignment mark

P2: Substrate alignment mark

PM: First Positioner

PS: Projection system

PS2: Position sensor

PW: Second locator

SO: Source Collector Module

W: Substrate

WT: Substrate table

Embodiments of the invention will now be described by way of example only with reference to the accompanying schematic drawings, in which corresponding element symbols indicate corresponding parts and in which: FIG. 1 depicts a lithography apparatus according to an embodiment of the invention; FIG. 2 is a more detailed view of the lithography apparatus; FIG. 3 is a more detailed view of a source collector module SO of the apparatus of FIGS. 1 and 2; FIG. 4 is a schematic view of a radiation sensor; and FIG. 5 is a schematic view of a substrate. FIG. 6 is a schematic diagram of an illuminated area; FIG. 7 is a schematic diagram of a configuration of a sensor element according to an embodiment of the present invention; FIG. 8 is a schematic diagram of an alternative configuration of a sensor element according to an embodiment of the present invention; FIG. 9 is a schematic diagram of a configuration of a sensor element according to a comparative example; and FIG. 10 is a graph showing the relationship between the lateral position of the illuminated area and the intensity of the patterned radiation beam. The features and advantages of the present invention will become more apparent from the detailed description set forth below in conjunction with the drawings, in which similar element symbols always identify corresponding elements. In the drawings, the same reference numerals generally indicate identical, functionally similar and/or structurally similar elements.

FIG. 1 schematically depicts a lithography apparatus 100 including a source collector module SO according to one embodiment of the present invention. The apparatus comprises: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., EUV radiation); a support structure (e.g., a mask stage) MT constructed to support a patterning device (e.g., a mask or a multiplying mask) MA and connected to a first positioner PM configured to accurately position the patterning device; a substrate stage (e.g., a wafer stage) WT constructed to hold a substrate (e.g., an anti-etchant coated wafer) W and connected to a second positioner PW configured to accurately position the substrate; and a projection system (e.g., a reflective projection system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

Illumination systems may include various types of optical components for directing, shaping or controlling radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof.

The support structure MT holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithography apparatus, and other conditions such as, for example, whether the patterning device is held in a vacuum environment. The support structure may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be, for example, a frame or a table, which may be fixed or movable as required. The support structure may ensure that the patterning device is in a desired position, for example, relative to a projection system.

The term "patterning device" should be interpreted broadly to mean any device that can be used to impart a pattern to a radiation beam in its cross-section so as to produce a pattern in a target portion of a substrate. The pattern imparted to the radiation beam may correspond to a specific functional layer in a device (e.g., an integrated circuit) produced in the target portion.

Patterned devices can be transmissive or reflective. Examples of patterned devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase shift, and attenuated phase shift, as well as various hybrid mask types. One example of a programmable mirror array uses a matrix arrangement of mirror facets, each of which can be individually tilted to reflect an incident radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam reflected by the mirror array.

Similar to the illumination system, the projection system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, appropriate to the exposure radiation used or to other factors such as the use of a vacuum. A vacuum may be required for EUV radiation since other gases may absorb too much radiation. Therefore, a vacuum environment may be provided to the entire beam path by means of vacuum walls and a vacuum pump.

As depicted here, the device is of the reflective type (e.g., using a reflective reticle).

Lithography equipment may be of a type having two (dual stage) or more substrate stages (and/or two or more mask stages). In such "multi-stage" machines, the additional stages may be used in parallel, or preparatory steps may be performed on one or more stages while one or more other stages are being used for exposure.

Referring to FIG. 1 , the illuminator IL receives an extreme ultraviolet radiation beam from a source collector module SO. Methods for generating EUV light include, but are not necessarily limited to, converting a material having at least one element (e.g., xenon, lithium, or tin) into a plasma state using one or more emission lines in the EUV range. In one such method (often referred to as laser produced plasma "LPP"), the desired plasma may be generated by irradiating a fuel (e.g., a droplet, stream, or cluster of material having the desired spectral line emitting element) with a laser beam. The source collector module SO may be a component of an EUV radiation system including a laser (not shown in FIG. 1 ) for providing a laser beam for exciting the fuel. The resulting plasma emits output radiation, such as EUV radiation, which is collected using a radiation collector disposed in a source collector module. For example, when a _CO2 laser is used to provide the laser beam for fuel excitation, the laser and source collector module can be separate entities.

In these cases, the laser is not considered to form part of the lithography apparatus and the laser beam is delivered from the laser to the source collector module by means of a beam delivery system comprising, for example, suitable steering mirrors and/or beam expanders. In other cases, for example when the source is a discharge produced plasma EUV generator (often referred to as a DPP source), the source may be an integral part of the source collector module.

The illuminator IL may include an adjuster for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer radial extent and/or the inner radial extent (typically referred to as σouter and σinner, respectively) of the intensity distribution in the pupil plane of the illuminator may be adjusted. In addition, the illuminator IL may include various other components, such as a faceted field mirror device and a faceted pupil mirror device. The illuminator may be used to adjust the radiation beam to have a desired uniformity and intensity distribution in its cross-section.

A radiation beam B is incident on a patterning device (e.g., a mask) MA held on a support structure (e.g., a mask table) MT and is patterned by the patterning device. After reflection from the patterning device (e.g., a mask) MA, the radiation beam B passes through a projection system PS which focuses the beam onto a target portion C of a substrate W. By means of a second positioner PW and a position sensor PS2 (e.g., an interferometric device, a linear encoder or a capacitive sensor), the substrate table WT can be accurately moved, for example, so that different target portions C are positioned in the path of the radiation beam B. Similarly, a first positioner PM and a further position sensor PS1 can be used to accurately position the patterning device (e.g., a mask) MA relative to the path of the radiation beam B. The mask alignment marks M1, M2 and the substrate alignment marks P1, P2 can be used to align the patterning device (e.g., mask) MA and the substrate W.

The depicted device may be used in at least one of the following modes:

1. In step mode, the support structure (e.g., mask table) MT and substrate table WT are kept substantially stationary (i.e., single static exposure) while the entire pattern imparted to the radiation beam is projected onto the target portion C at one time. The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed.

2. In scanning mode, the support structure (e.g., mask stage) MT and the substrate stage WT are scanned synchronously while the pattern imparted to the radiation beam is projected onto the target portion C (i.e., single dynamic exposure). The speed and direction of the substrate stage WT relative to the support structure (e.g., mask stage) MT can be determined by the magnification (reduction) and image inversion characteristics of the projection system PS.

3. In another mode, the support structure (e.g., mask table) MT, holding the programmable patterning device, is kept substantially stationary while the pattern imparted to the radiation beam is projected onto the target portion C, and the substrate table WT is moved or scanned. In this mode, a pulsed radiation source is typically used, and the programmable patterning device is updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography using programmable patterning devices (such as programmable mirror arrays of the type mentioned above).

Combinations and/or variations of the modes of use described above or entirely different modes of use may also be used.

FIG2 shows the apparatus 100 in more detail, which includes a source collector module SO, an illumination system IL, and a projection system PS. The source collector module SO is constructed and configured so that a vacuum environment can be maintained in an enclosure 220 of the source collector module SO. The EUV radiation emitting plasma 210 may be formed by a discharge generating plasma source. EUV radiation may be generated by a gas or vapor (e.g., Xe gas, Li vapor, or Sn vapor), wherein the ultrahot plasma 210 is generated to emit radiation in the EUV range of the electromagnetic spectrum. For example, the ultrahot plasma 210 is generated by a discharge that causes at least a partially ionized plasma. To efficiently generate radiation, a partial pressure of, for example, 10 Pascals of Xe, Li, Sn vapor or any other suitable gas or vapor may be required. In one embodiment, an excited tin (Sn) plasma is provided to generate EUV radiation.

Radiation emitted by hot plasma 210 is transmitted from source chamber 211 to collector chamber 212 through an optional gas barrier or contaminant trap 230 (also referred to as a contaminant barrier or foil trap in some cases) positioned in or behind an opening in source chamber 211. Contaminant trap 230 may include a channel structure. Contaminant trap 230 may also include a gas barrier, or a combination of a gas barrier and a channel structure. As is known in the art, the contaminant trap or contaminant barrier 230 further indicated herein includes at least a channel structure.

The collector chamber 212 may include a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation that traverses the collector CO may be reflected from the grating spectrum filter 240 to be focused in a virtual source point IF. The virtual source point IF is usually referred to as an intermediate focus, and the source collector module is configured so that the intermediate focus IF is located at or near an opening 221 in the enclosure 220. The virtual source point IF is an image of the radiation emitting plasma 210.

The radiation then traverses the illumination system IL, which may include a faceted field mirror device 22 and a faceted pupil mirror device 24, which are configured to provide the desired angular distribution of the radiation beam 21 at the patterning device MA and the desired uniformity of the radiation intensity at the patterning device MA. After reflection of the radiation beam 21 at the patterning device MA held by the support structure MT, a patterned beam 26 is formed and is imaged by the projection system PS via reflective elements 28, 30 onto a substrate W held by a wafer stage or substrate table WT.

More elements than shown may typically be present in the illumination optics unit IL and the projection system PS. Depending on the type of lithography apparatus, a grating spectral filter 240 may be present as appropriate. Additionally, more mirrors may be present than shown in the figures, for example, there may be 1 to 6 additional reflective elements in the projection system PS than shown in FIG. 2 .

The collector optics CO illustrated in FIG2 is depicted as a nested collector with grazing incidence reflectors 253, 254 and 255 as an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254 and 255 are arranged axially symmetrically around the optical axis O, and this type of collector optics CO is preferably used in conjunction with a discharge produced plasma source (which is often referred to as a DPP source).

Alternatively, the source collector module SO may be a component of an LPP radiation system as shown in FIG3 . The laser LA is configured to deposit laser energy into a fuel such as xenon (Xe), tin (Sn) or lithium (Li), thereby producing a highly ionized plasma 210 having an electron temperature of tens of electron volts. High energy radiation produced during deexcitation and recombination of this plasma is emitted from the plasma, collected by the near normal incidence collector optics CO, and focused onto an opening 221 in the enclosure 220.

FIG. 4 is a schematic diagram of a radiation sensor 10 of a lithography apparatus 100. FIG. 4 shows a substrate table WT of the lithography apparatus 100. The substrate table WT is configured to hold a substrate W.

As shown in FIGS. 1 and 2 , the lithography apparatus 100 includes a projection system PS. The projection system PS is configured to project a radiation beam B to form an illuminated area 11 at a substrate level (shown in FIG. 5 ).

As shown in FIG. 4 , in one embodiment, the substrate table WT includes a radiation sensor 10. The radiation sensor 10 is configured to detect a radiation beam B. The radiation sensor 10 is configured to detect characteristics of the radiation beam B at the substrate level.

For example, in one embodiment, the radiation sensor 10 is configured to measure how the intensity of the radiation beam B varies across the illuminated region 11. In one embodiment, the radiation sensor 10 is configured to measure the wavefront of the radiation beam B at the substrate step. For example, the radiation sensor 10 may be configured to measure Zernike aberrations. In one embodiment, the radiation sensor 10 is configured to measure high-order Zernike aberrations and/or low-order Zernike aberrations.

As mentioned above, the radiation beam B may be EUV radiation. As shown in FIGS. 1 and 2 , the patterning device MA held by the support structure MT may be configured to reflect the radiation beam B. Alternatively, the radiation beam B modulated by the illumination system IL may be deep ultraviolet (DUV) radiation. As shown in FIG. 4 , in one embodiment, the patterning device MA is transmissive. The patterning device MA is configured to transmit the radiation beam B when it imparts a pattern to the radiation beam B. The present invention is applicable to the lithography apparatus 100, whether it uses EUV radiation or DUV radiation. The present invention is compatible with either a transmissive patterning device MA or a reflective patterning device MA.

As mentioned above, the projection system PS is configured to project a radiation beam B to form an illuminated area 11 at the level of the substrate. The illuminated area 11 has an elongated shape. FIG. 5 is a schematic diagram of the illuminated area 11 relative to the substrate W. In one embodiment, the shape of the radiation sensor 10 in a plan view substantially matches the shape of the illuminated area 11. As shown in FIG. 5, in one embodiment, the illuminated area 11 has a long edge 12 and a short edge 13. The illuminated area 11 defines a longitudinal direction 15 and a transverse direction 16 perpendicular to the longitudinal direction.

FIG. 6 is a close-up view of the illuminated area 11 shown in FIG. 5 . In FIG. 6 , the longitudinal direction 15 and the transverse direction 16 are shown. In one embodiment, the illuminated area 11 has a curved shape. When the illuminated area 11 has a curved shape, the transverse direction 16 at one point along the elongated shape may not be parallel to the transverse direction at another point along the elongated shape. The longitudinal direction 15 follows a curve. FIG. 6 also shows a centerline 14 along the middle of the illuminated area 11. The centerline 14 is formed by the trajectory of the midpoints between the long edges 12 in the transverse direction 16.

The radiation sensor 10 is configured to measure how the radiation beam B varies along the length of the illuminated area 11. The radiation sensor 10 includes a plurality of sensor elements 17 configured to detect the radiation beam B. The sensor elements 17 are arranged along the longitudinal direction 15. This allows the sensor elements 17 of the radiation sensor 10 to measure how the radiation beam B varies along the illuminated area 11.

The sensor element may be arranged to follow one of the center line 14 or the long edge 12 of the illuminated area 11. When the illuminated area has a curved elongated shape, the sensor element may be arranged to follow the same curve.

As shown in FIGS. 5 and 6 , in one embodiment, the elongated shape is curved. In an alternative embodiment, the projection system PS is configured to project the radiation beam B to form an illuminated area 11 having an elongated rectangular shape. For example, when the radiation beam B is DUV radiation, a rectangular illuminated area 11 may be provided.

FIG. 7 is a schematic diagram showing the configuration of the sensor elements 17 of the radiation sensor 10 according to the present invention. FIG. 7 also shows how the configuration of the elements 17 is compared with a comparative example. In FIG. 7 , the comparison dots 27 show the positions of the sensor elements according to a comparative example. In the comparative example, the sensor elements are configured to closely follow the curve of the elongated shape of the illuminated area 11.

As shown in FIG. 7 , in one embodiment, a plurality of sensor elements 17 are arranged at different distances from one of the long edges 12 of the elongated shape of the illuminated area 11 in the transverse direction 16. The plurality of sensor elements 17 are offset (in the transverse direction) from the positions shown in the comparative example. In FIG. 7 , arrows 18 show how the position of each sensor element 17 changes relative to the comparison dot 27.

It is contemplated that an embodiment of the present invention reduces the time spent measuring how the radiation beam B varies throughout the illuminated area 11. It is necessary to measure how the radiation beam B varies along the transverse direction 16 of the illuminated area 11 (i.e. in the width direction). This requires taking measurements at a plurality of different positions along the transverse direction 16. By providing sensor elements 17 at different transverse positions, the radiation beam B is measured at different transverse positions simultaneously. In contrast, the comparative example shown in FIG. 7 would require more measurements using the entire radiation sensor 10 displaced in the transverse direction relative to the illuminated area 11. A larger number of measurements would take longer.

The decay of the radiation beam B needs to be measured. The decay of the radiation beam B is related to how the radiation beam changes (e.g., in terms of intensity or other characteristics) along the lateral direction of the illuminated area 11. With a layout as shown in the comparative example in FIG. 7, the decay measurement requires two or more scans at different lateral positions in the illuminated area 11. This results in a loss of throughput. It is contemplated that an embodiment of the present invention uses a small number of measurements (e.g., only a single scan) to capture the decay.

As shown in FIG. 7 , in one embodiment, at least one of the sensor elements 17 is offset in the transverse direction 16 toward the concave side of the elongated shape. In the embodiment shown in FIG. 7 , the first, fourth, and seventh sensor elements 17 (from left to right in FIG. 7 ) are offset toward the concave side. This is indicated by the downward arrow 18. As shown in FIG. 7 , in one embodiment, at least one of the sensor elements 17 is offset in the transverse direction 16 toward the convex side of the elongated shape. In the embodiment shown in FIG. 7 , the second, third, fifth, and sixth (from left to right in FIG. 7 ) sensor elements 17 are offset toward the convex side. This is indicated by the upward arrow 18 in FIG. 7 . The offsets are relative to a comparative example following the center line 14 of the illuminated area 11 .

By providing offsets towards both the concave and convex sides, a single scan includes measurements from at least three lateral positions in the illuminated area 11.

In the example shown in FIG. 7 , the measurement consists of two different transverse positions. The second, third, fifth and sixth sensor elements 17 correspond to the first transverse position. The first, fourth and seventh elements 17 correspond to the second transverse position. Instead of measuring seven different longitudinal positions at a single transverse position, at least one measurement is performed at a plurality of different transverse positions. In one embodiment, at least one of the sensor elements 17 is not offset. This makes it possible to perform measurements of three different transverse positions simultaneously.

The measurements corresponding to the different sensor elements 17 can be interpolated to provide information about the variation of the radiation beam B across the illumination shape 11 both in the longitudinal and in the transverse direction.

FIG8 shows the configuration of the sensor element 17 of the radiation sensor 10. The configuration shown in FIG8 is an alternative to the configuration shown in FIG7. FIG8 also shows a comparison dot 27 showing the configuration of the sensor element in the comparison example.

The configurations shown in FIG. 7 and FIG. 8 differ from each other in that the configuration shown in FIG. 7 is symmetrical, while the configuration shown in FIG. 8 is sparse or asymmetrical. As shown in FIG. 7 , in one embodiment, the sensor elements 17 are arranged symmetrically around a symmetry axis extending in the transverse direction 16. In the example shown in FIG. 7 , the symmetry axis passes through the center (fourth) sensor element 17 shown in FIG. 7 in the transverse direction.

Alternatively, as shown in FIG. 8 , in one embodiment, the sensor elements 17 are asymmetrically arranged around an axis extending in the transverse direction halfway along the sensor element 17 in the longitudinal direction. For example, the third sensor element 17 is offset toward the convex side, while the fifth sensor element 17 is not offset.

The configurations shown in Figures 7 and 8 are examples of ways in which the sensor element 17 may be configured. However, other configurations are possible while providing the advantage of measuring the radiation beam B at multiple lateral positions simultaneously.

In one embodiment, the sensor element 17 is arranged in a sawtooth pattern. For example, when the elongated shape is rectangular, the sensor element 17 can be arranged in a simple sawtooth pattern to measure at two different lateral positions simultaneously.

FIG. 9 shows a radiation sensor 10 in which a comparison dot 27 corresponds to a sensor element. The comparison example shown in FIG. 9 may be a sensor for an illuminated area 11 having a rectangular shape. The sensor elements are all positioned at the same lateral position. This makes it necessary to perform multiple measurements in order to measure multiple lateral positions.

In contrast, providing the sensor elements 17 in a sawtooth pattern configuration allows for multiple lateral positions to be measured simultaneously.

In one embodiment, the center sensor element 17 is not offset or is offset toward the concave side. In one embodiment, one of the sensor elements 17 centrally positioned along the longitudinal direction is offset more from the one of the long edges 12 along the concave side of the elongated shape in the transverse direction than another of the sensor elements 17. FIG. 7 shows the center sensor element 17 offset toward the concave side (downward in FIG. 7). Meanwhile, FIG. 8 shows the center sensor element 17 not offset. By not providing an offset or providing an offset toward the concave side of the center sensor element 17, the lateral range of the sensor element 17 (in the upward and downward directions of FIG. 7 and FIG. 8) is not increased by the offset. It is contemplated that one embodiment of the present invention reduces the lateral range of the radiation sensor 10.

However, in an alternative embodiment, the central sensor element 17 may be offset towards the convex side.

As mentioned above, in one embodiment, the lithography apparatus includes an illuminator IL. The illuminator IL is configured to provide a projection radiation beam. In one embodiment, the illuminator IL is configured to provide a radiation beam B such that its intensity varies nominally trapezoidally in the transverse direction 16 of the elongated shape. FIG. 10 is a graph showing the relationship between the transverse position and the intensity of the radiation beam. The x-axis corresponds to the position along the transverse direction 16 of the illuminated area 11. The y-axis represents the intensity of the radiation beam B. The transverse position of the long edge 12 of the elongated shape is shown in FIG. 10. FIG. 10 shows the trapezoidal shape of the radiation beam B.

FIG. 10 shows a plateau 18 of the intensity of the radiation beam B in the transverse direction 16. The central region 19 of the illuminated region 11 corresponds to the plateau 18 of the intensity. In one embodiment, the sensor elements 17 are arranged so that they are all arranged within the nominal plateau 18 of the intensity in a trapezoid. It is contemplated that one embodiment of the invention improves the accuracy of measurements made simultaneously at different transverse positions.

Of course, the radiation beam B may not have a perfect trapezoidal shape in the transverse direction. In one embodiment, the radiation beam B has a Gaussian distribution in the transverse direction. The radiation beam B may have a target shape corresponding to a nominal trapezoidal shape. The difference from the nominal trapezoidal shape may be detected by measurements made by the radiation sensor 10. The lithography apparatus 100 may be adjusted to compensate for the deviation from the nominal shape of the radiation shape B. For example, the position and/or orientation of the optical elements may be adjusted based on the measurements made by the radiation sensor 10. In one embodiment, the projection system PS is configured to correct aberrations of the wavefront measured using the radiation sensor 10.

It is not necessary for the radiation beam B to have a trapezoidal shape in the transverse direction. Some other shapes of the beam are also possible. In one embodiment, the radiation beam B has a plateau of intensity in the transverse direction.

In the examples shown in FIGS. 7 and 8 , some sensor elements 17 are offset in one direction, while other sensor elements 17 are offset in the opposite direction. In one embodiment, the amount of offset is the same for all offset sensor elements 17. In the example shown in FIG. 7 , all sensor elements except the center sensor element 17 are offset. In one embodiment, the magnitude of the offset is the same for each of the offset sensor elements 17. In other words, the distance between the sensor element 17 and the comparison dot 27 is the same for the first, second, third, fifth, sixth, and seventh sensor elements 17.

In the example shown in FIG. 8 , each of the first, second, third, fourth, sixth, and seventh sensor elements 17 is offset the same distance from its corresponding comparison point 27. In one embodiment, the possible positions of the sensor elements 17 are discretized. For example, a grid of points separated by uniformly spaced steps is provided. Each sensor element 17 is offset by only one step (or not at all). This helps to simplify the configuration of the sensor elements 17. In one embodiment, each of the sensor elements 17 offset from the long edge 12 of the elongated shape in the transverse direction 16 is offset by substantially the same amount. In an alternative embodiment, each sensor element 17 is offset by two or more steps.

As shown in FIGS. 7 and 8 , in one embodiment, the sensor elements 17 are uniformly spaced along the longitudinal direction 15. It is contemplated that one embodiment of the present invention achieves better fit quality and/or reduced sensitivity to sensor noise. However, this is not necessarily the case. The sensor elements 17 may be spaced at different intervals along the longitudinal direction.

In one embodiment, the radiation sensor 10 includes an imaging device. For example, the imaging device can be a charge coupled device (CCD). A single imaging device can be used for a plurality of sensor elements 17. The sensor elements 17 correspond to different positions that can be measured simultaneously. In one embodiment, the radiation sensor 10 includes one or more gratings. In one embodiment, each sensor element 17 corresponds to a separate grating. In one embodiment, each sensor element corresponds to a separate opening within the coverage area of the radiation sensor 10. Each opening allows the radiation beam B to reach the grating and then reach the imaging 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, such as manufacturing integrated optical systems, guide and detection patterns for magnetic resonance memory, flat panel displays, liquid crystal displays (LCDs), thin film heads, etc. Those skilled in the art will understand that in the context of such alternative applications, any use of the terms "wafer" or "die" herein may be considered synonymous with the more general terms "substrate" or "target portion," respectively. The substrates mentioned herein may be processed, for example, in a coating and development system (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool, and/or an inspection tool, before or after exposure. Where applicable, the disclosures herein may be applied to these and other substrate processing tools. In addition, a substrate may be processed more than once (for example, to produce a multi-layer IC), so that the term substrate as used herein may also refer to a substrate that already contains multiple processed layers.

The term "lens" may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components, when the context permits.

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. For example, the sensor element 17 may be configured in a manner different from that shown in FIGS. 7 and 8 .

Terms:

Item 1. A lithography apparatus comprising: a substrate stage configured to hold a substrate; and a projection system configured to project a radiation beam to form an illuminated area having an elongated shape at the substrate level, the elongated shape having long edges and short edges and defining a longitudinal direction and a transverse direction perpendicular to the longitudinal direction; wherein the substrate stage comprises a plurality of sensor elements configured to detect the radiation beam, the sensor elements being arranged along the longitudinal direction, wherein a plurality of the sensor elements are arranged at different distances from one of the long edges of the elongated shape in the transverse direction.

Clause 2. A lithography apparatus as claimed in clause 1, wherein the elongated shape is a rectangle.

Clause 3. A lithography apparatus as claimed in clause 1, wherein the elongated shape is curved.

Item 4. A lithography apparatus as in Item 3, wherein one of the sensor elements centrally located along the longitudinal direction is offset more from the one of the long edges toward a concave side of the elongated shape in the transverse direction than another one of the sensor elements.

Clause 5. A lithography apparatus as in clause 3 or 4, wherein at least one of the sensor elements is offset in the lateral direction toward a concave side of the elongated shape, and at least one of the sensor elements is offset in the lateral direction from one of the long edges of the elongated shape toward a convex side.

Clause 6. A lithography apparatus as claimed in any preceding clause, wherein at least one of the sensor elements is offset differently in the transverse direction than another of the sensor elements relative to a trajectory of a midpoint between the edges of the elongated shape.

Clause 7. A lithography apparatus as claimed in any preceding clause, wherein the sensor elements are arranged in a sawtooth pattern.

Clause 8. A lithography apparatus as in any preceding clause, wherein the sensor elements are arranged asymmetrically about an axis extending in the transverse direction halfway along the sensor elements in the longitudinal direction.

Item 9. A lithography apparatus as in any one of items 1 to 7, wherein the sensor elements are arranged symmetrically around a symmetry axis extending in the transverse direction.

Clause 10. A lithography apparatus as in any preceding clause, wherein each of the sensor elements offset in the lateral direction from the one of the long edges of the elongated shape is offset by substantially the same amount.

Clause 11. A lithography apparatus as claimed in any preceding clause, wherein the sensor elements are equally spaced along the longitudinal direction.

Clause 12. A lithography apparatus as in any preceding clause, comprising: an illuminator configured to provide a projected radiation beam, wherein the projection beam is the radiation beam projected by the projection system.

Clause 13. A lithography apparatus as claimed in clause 12, wherein the illuminator is configured to provide the projection beam such that its intensity varies nominally trapezoidally in the transverse direction of the elongated shape.

Clause 14. A lithography apparatus as claimed in clause 13, wherein the sensor elements are arranged so that they are all arranged within a nominal flat line region of the intensity of the trapezoid.

Clause 15. A lithography apparatus as in any preceding clause, comprising: a support structure configured to support a patterning device for patterning the radiation beam according to a desired pattern, wherein the patterned beam is a radiation beam projected by the projection system.

Clause 16. A substrate stage, which belongs to a lithography apparatus as in any of the preceding clauses.

Item 17. A method for detecting a radiation beam in a lithography apparatus, the method comprising: providing a projected radiation beam; projecting the projection beam to form an illuminated area having an elongated shape at a substrate level, the elongated shape having long edges and short edges and defining a longitudinal direction and a transverse direction perpendicular to the longitudinal direction; detecting the radiation beam at the substrate level using a plurality of sensor elements, the sensor elements being arranged along the longitudinal direction, wherein a plurality of the sensor elements are arranged at different distances from one of the long edges of the elongated shape in the transverse direction.

10: Radiation sensor

17: Sensor components

18: Downstream arrow/intensity platform

27: Compare dots

Claims (15)

A substrate stage configured to hold a substrate, comprising: a plurality of sensor elements configured to detect a radiation beam from a projection system, the radiation beam forming an illuminated area having an elongated shape at the substrate level, the elongated shape having long edges and short edges and defining a longitudinal direction and a transverse direction perpendicular to the longitudinal direction, the sensor elements being arranged along the longitudinal direction, wherein the plurality of the sensor elements are arranged at different distances from one of the long edges of the elongated shape in the transverse direction. A substrate stage as claimed in claim 1, wherein the elongated shape is rectangular or curved. A substrate stage as claimed in claim 1, wherein the elongated shape is curved. A substrate stage as claimed in claim 3, wherein one of the sensor elements centrally located along the longitudinal direction is offset more from one of the long edges toward a concave side of the elongated shape in the transverse direction than another of the sensor elements. A substrate stage as claimed in claim 3 or 4, wherein at least one of the sensor elements is offset in the lateral direction toward a concave side of the elongated shape, and at least one of the sensor elements is offset in the lateral direction from one of the long edges of the elongated shape toward a convex side. A substrate stage as claimed in any one of claims 1 to 4, wherein at least one of the sensor elements is offset differently in the transverse direction than another of the sensor elements relative to a locus of a midpoint between the edges of the elongated shape. A substrate stage as claimed in any one of claims 1 to 4, wherein the sensor elements are arranged in a saw-tooth pattern, or/and wherein the sensor elements are arranged asymmetrically around an axis extending in the transverse direction halfway along the sensor elements in the longitudinal direction. A substrate stage as claimed in any one of claims 1 to 4, wherein the sensor elements are arranged symmetrically around a symmetry axis extending in the transverse direction. A substrate stage as claimed in any one of claims 1 to 4, wherein each of the sensor elements offset in the lateral direction from the one of the long edges of the elongated shape is offset by substantially the same amount. A substrate stage as claimed in any one of claims 1 to 4, wherein the sensor elements are equally spaced along the longitudinal direction. A lithography apparatus comprising a substrate stage as claimed in any one of claims 1 to 10. The lithography apparatus of claim 11 comprises: an illuminator configured to provide a projection radiation beam, wherein the projection radiation beam is the radiation beam projected by the projection system. A lithography apparatus as claimed in claim 12, wherein the illuminator is configured to provide the projected radiation beam such that its intensity varies nominally trapezoidally in the transverse direction of the elongated shape. A lithography apparatus as claimed in claim 13, wherein the sensor elements are arranged so that they are all arranged within a nominal plateau of the intensity of the trapezoid. A method for detecting a radiation beam in a lithography apparatus, the method comprising: providing a projected radiation beam; projecting the projected radiation beam to form an illuminated area having an elongated shape at a substrate level, the elongated shape having long edges and short edges and defining a longitudinal direction and a transverse direction perpendicular to the longitudinal direction; detecting the projected radiation beam using a plurality of sensor elements at the substrate level, the sensor elements being arranged along the longitudinal direction, wherein a plurality of the sensor elements are arranged at different distances from one of the long edges of the elongated shape in the transverse direction.