TW201946499A - System for testing a mirror such as a collector mirror and method of testing a mirror such as a collector mirror - Google Patents

Abstract

The present invention discloses a system configured to test a collector lens having a first focus and a second focus. The system includes a test radiation subsystem operable to direct test radiation from the second focus. Projected onto the collector mirror; a sensor subsystem operable to receive test radiation reflected from the collector mirror toward the first focus; and a radiation limiter subsystem operable to pass The test radiation received by the sensor is limited to test radiation reflected from a restricted portion of the collector mirror; a control subsystem operable to control the radiation limiter subsystem along a series of different positions. A movement, thereby limiting the test radiation, as received by the sensor, to test radiation reflected from different restricted portions of a series of collector mirrors.

Description

System for testing a mirror such as a collector mirror and method for testing a mirror such as a collector mirror

The present invention relates to a system and method for testing a face mirror. As an example of such a mirror, a collector mirror may be mentioned, such as a collector mirror used in EUV radiation sources.

A lithographic apparatus is a machine that applies a desired pattern to a substrate, typically to a target portion of the substrate. Lithography devices can be used, for example, in the manufacture of integrated circuits (ICs). In that case, patterned devices, which are alternatively referred to as photomasks or reduction masks, can be used to generate circuit patterns to be formed on individual layers of the IC. This pattern can be transferred to a target portion (such as a portion containing a die, a die, or several die) on a substrate (eg, a silicon wafer). Pattern transfer is usually performed by imaging onto a radiation-sensitive material (resist) layer provided on a substrate. In general, a single substrate will contain a network of adjacent target portions that are sequentially patterned.

Lithography is widely regarded as a key step in the manufacture of ICs and other devices and / or structures. However, as the size of features made using lithography becomes smaller and smaller, lithography is becoming a more decisive factor for enabling the manufacture of small ICs or other devices and / or structures.

A theoretical estimate 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, k ₁ is the program-dependent adjustment factor, also known as the Rayleigh constant, and CD is the feature size (or criticality) of the printed feature size). It can be seen from equation (1) that the reduction of 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 decreasing the value of k ₁ .

To shorten the exposure wavelength and therefore the minimum printable size, the use of extreme ultraviolet (EUV) radiation sources has been proposed. EUV radiation is electromagnetic radiation having a wavelength in the range of 5 nm to 20 nm, for example in the range of 13 nm to 14 nm. It has further been proposed that EUV radiation having a wavelength of less than 10 nm can be used, for example in the range of 5 nm to 10 nm, such as 6.7 nm or 6.8 nm. Possible sources include laser-generated plasma (LPP) sources, but other types of sources are possible.

An example of the current progress in the development of LPP sources for EUV lithography is described in the paper "High power LPP EUV source system development status" by Benjamin Szu-Min Lin, David Brandt, Nigel Farrar, SPIE Conference Records Volume 7520, Lithography Asia 2009, December 2009 (SPIE Digital Library Reference DOI: 10.1117 / 12.839488). In lithography systems, the source device will usually be contained within its own vacuum enclosure, while providing a small exit aperture to couple the EUV radiation beam into the optical system where the radiation will be used.

In order to be suitable for high-resolution patterning of lithography, when the EUV radiation beam reaches the reduction mask, the EUV radiation beam must be adjusted to obtain desired parameters such as the uniformity of the intensity distribution and angular distribution. Examples of lighting systems are described in US Patent Application Publication Nos. 2005 / 0274897A1 (Carl Zeiss / ASML) and 2011 / 0063598A (Carl Zeiss). An example system includes a "fly-eye" illuminator that transforms a highly non-uniform intensity profile of an EUV source into a more uniform and controllable source.

For good imaging performance, it is important that the collector mirror as used in the EUV source has a sufficiently high and uniform reflectance. Such collector lenses may be contaminated due to debris generated by the EUV radiation generating program. Thus, the collector lens may be periodically subjected to a cleaning procedure, followed by a detection or test procedure in order to evaluate the reflectance.

Known methods for determining reflectance are considered to be quite time consuming and expensive. The aforementioned inspection and testing may also be required for EUV radiation sources or other mirrors used in lithographic devices. Similarly, known methods for determining the reflectivity of such mirrors can also be energy intensive and expensive.

The aspect of the embodiments of the present invention is to provide an alternative system and method for testing a collector mirror of an EUV source.

According to one aspect of the present invention, a system configured to test a collector mirror having a first focus and a second focus is provided. The system includes: a test radiation subsystem operable to test Radiation is projected from the second focus onto the collector mirror; a sensor subsystem operable to receive test radiation reflected from the collector mirror toward the first focus; and a radiation limiter subsystem, which Operable to limit the test radiation as received by the sensor to test radiation reflected from a restricted portion of the collector mirror; a control subsystem operable to control the radiation limiter subsystem along Moving in one of a series of different positions, thereby limiting the test radiation as received by the sensor to the test radiation reflected from each of a series of different restricted portions of the collector mirror.

According to another aspect of the present invention, a method for testing a collector mirror having a first focus and a second focus is provided. The method includes: projecting test radiation from the second focus onto the collector mirror; Test radiation received by a sensor reflected from the collector mirror toward the first focus; and testing to limit the test radiation, as received by the sensor, to reflection from a restricted portion of the collector mirror Radiation; control the radiation limiting system to move along one of a series of different positions, thereby limiting the test radiation as received by the sensor to a test of reflection from each of a series of different restricted portions of the collector mirror radiation.

According to yet another aspect of the present invention, a system configured for testing a mirror is provided. The system includes:
A test radiation subsystem operable to project test radiation onto the mirror;
A sensor subsystem operable to receive test radiation reflected from the mirror; and a radiation limiter subsystem operable to limit the test radiation as received by the sensor subsystem to Test radiation reflected from a restricted part of the mirror;
A control subsystem operable to control the radiation limiter subsystem to move along one of a series of different positions, thereby limiting the test radiation as received by the sensor subsystem to the surface of the mirror. A series of test radiation reflected by different restricted sections.

These aspects of the present invention, as well as its various optional features and implementations, will be understood by those skilled in the art from the description of the following examples.

FIG. 1 schematically depicts a lithographic system 100 according to an embodiment of the present invention. The lithographic system includes a lithographic device and an EUV radiation source, and the EUV radiation source is configured to generate EUV radiation, such as an EUV radiation beam. In the embodiment as shown, the EUV radiation source comprises a source collector module SO. In the embodiment as shown, the lithographic scanning device comprises: an illumination system (illuminator) IL configured to regulate a radiation beam B (e.g. EUV radiation); a support structure (e.g. a mask table) MT, which is Constructed to support a patterned device (such as a reticle or a reduction mask) MA and connected to a first positioner PM configured to accurately position the patterned device; a substrate table (such as a wafer table) WT, which is Constructed to hold a substrate (such as a resist-coated wafer) W and connect to a second positioner PW configured to accurately position the substrate; and a projection system (such as a reflective projection system) PS, which is configured to A pattern imparted to the radiation beam B by the patterning device MA is projected onto a target portion C (for example, containing one or more dies) of the substrate W.

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

The term "patterned device" should be interpreted broadly to mean any device that can be used to impart a pattern to a radiation beam in a cross-section of the radiation beam so as to create 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 such as an integrated circuit generated in the target portion.

The patterned device may be transmissive or reflective. Examples of patterned devices include photomasks, programmable mirror arrays, and programmable LCD panels. Masks are well known to us in lithography and include mask types such as binary, alternating phase shift, and attenuation phase shift, as well as various hybrid mask types. One example of a programmable mirror array uses a matrix configuration of facets, each of which can be individually tilted so that the incident radiation beam is reflected in different directions. The tilted mirror imparts a pattern to the radiation beam reflected by the mirror matrix.

Similar to lighting systems, projection systems may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components suitable for the exposure radiation used or other factors such as the use of vacuum, Or any combination thereof. Vacuum may be needed for EUV radiation because other gases may absorb too much radiation. Therefore, a vacuum environment and a vacuum pump can be used to provide a vacuum environment to the entire beam path.

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

The lithographic apparatus may be of a type having two (dual stage) or more than two substrate stages (and / or two or more photomask stages). In such "multi-stage" machines, additional stages may be used in parallel, or preliminary steps may be performed on one or more stages while one or more other stages are used for exposure.

Referring to FIG. 1, the illuminator IL receives an extreme ultraviolet radiation beam from a source collector module SO of an EUV radiation source. Methods to generate EUV light include, but are not necessarily limited to, using one or more emission lines in the EUV range to convert the material into a plasma state with at least one element, such as xenon, lithium, or tin. In one such method, often referred to as laser-generated plasma "LPP", a laser beam can be used to irradiate fuel such as droplets, streams, or clusters of materials with the required emission elements Generate the required plasma. The source collector module SO may be part of an EUV radiation system including a laser not shown in FIG. 1, which is used to provide a laser beam that excites 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 using a CO ₂ laser to provide a laser beam for fuel excitation, the laser and EUV radiation sources may be separate entities.

In such cases, the laser is not considered to form part of the lithography system, and the radiation beam is transmitted from the laser to the source collector mode by means of a beam delivery system including, for example, a suitable guide mirror and / or beam expander group. In other situations, for example, when the source is a discharge generating 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. Generally, at least the outer and / or inner radial range of the intensity distribution in the pupil plane of the illuminator can be adjusted (usually referred to as σouter and σinner, respectively). In addition, the illuminator IL may include various other components such as a faceted scene mirror device and a faceted pupil mirror device. The illuminator can be used to adjust the radiation beam to have the desired uniformity and intensity distribution in its cross section.

The radiation beam B is incident on a patterned device (eg, a photomask) MA that is fixed on a support structure (eg, a photomask table) MT, and is patterned by the patterned device. After being reflected from the patterned device (such as a photomask) MA, the radiation beam B is passed through the projection system PS, and the projection system PS focuses the beam onto the target portion C of the substrate W. With the second positioner PW and the position sensor PS2 (such as an interference measurement device, a linear encoder or a capacitive sensor), the substrate table WT can be accurately moved, for example to locate different targets in the path of the radiation beam B Part C. Similarly, the first positioner PM and another position sensor PS1 can be used to accurately position the patterned device (such as 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 may be used to align the patterned device (eg, the mask) MA and the substrate W.

The depicted device can be used in at least one of the following modes:
1. In the step mode, the supporting structure (such as the mask stage) MT and the substrate stage WT are kept substantially stationary, while the entire pattern imparted to the radiation beam is projected onto the target portion C at a time (ie, a single shot) Static exposure). Then, the substrate table WT is shifted in the X and / or Y direction, so that different target portions C can be exposed.
2. In the scan mode, the supporting structure (such as the mask stage) MT and the substrate stage WT are scanned synchronously, and the pattern imparted to the radiation beam is projected onto the target portion C (ie, a single dynamic exposure). The speed and direction of the substrate table WT relative to the supporting structure (such as a mask table) MT can be determined by the magnification (reduction rate) and image inversion characteristics of the projection system PS.
3. In another mode, when the pattern imparted to the radiation beam is projected onto the target portion C, the supporting structure (such as a photomask stage) is kept substantially stationary, thereby holding the programmable patterning device and moving Or scan the substrate table WT. In this mode, a pulsed radiation source is typically used, and the programmable patterned device is updated as needed after each movement of the substrate table WT or between successive radiation pulses during scanning. This mode of operation can be easily applied to maskless lithography using a programmable patterned device, such as a programmable mirror array of the type mentioned above.

Combinations and / or variations of the usage patterns described above or completely different usage patterns may also be used. The embodiment to be explained involves scanning, as in modes 2 and 3 just mentioned.

Although specific reference may be made herein to the use of lithographic devices in IC manufacturing, it should be understood that the lithographic devices described herein may have other applications, such as manufacturing integrated optical systems, guidance for magnetic domain memory Guide and detect patterns, flat panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, and more. Those skilled in the art should understand that in the context of the content of such alternative applications, any use of the term "wafer" or "die" herein may be considered separately from the more general term "substrate" or "target portion" Synonymous. The substrates mentioned herein may be processed before or after exposure in, for example, a coating development system (a tool that typically applies a resist layer to a substrate and develops the exposed resist), a metrology tool, and / or a detection tool. Where applicable, the disclosure herein can be applied to such and other substrate processing tools. In addition, the substrate may be processed more than once, for example to produce a multilayer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

FIG. 2 shows the system 100 in more detail, which includes an EUV radiation source including a source collector module SO, a lithographic scanning device including an illumination system IL, and a projection system PS. The source collector module SO of the EUV radiation source is constructed and configured so that a vacuum environment can be maintained in the enclosure structure 220 of the source collector module SO. The systems IL and PS are also contained in their own vacuum environment. An EUV radiation emitting plasma 210 may be formed from a laser-produced LPP plasma source. The function of the source collector module SO is to deliver the EUV radiation beam 20 from the plasma 210 so that it focuses on the virtual source point. The virtual source point is often referred to as an intermediate focus (IF), and the source collector module is configured such that the intermediate focus IF is located at or near the aperture 221 in the enclosure structure 220. The virtual source point IF is an image of the radiation-emitting plasma 210.

From the aperture 221 at the intermediate focus IF, radiation traverses the illumination system IL, which in this example includes a faceted scene mirror device 22 and a faceted pupil mirror device 24. These devices form a so-called "fly-eye" illuminator, which is configured to provide the desired angular distribution of the radiation beam 21 at the patterned device MA and the required uniformity of the radiation intensity at the patterned device MA. After the light beam 21 is reflected at the patterned device MA held by the support structure (photomask stage) MT, a patterned light beam 26 is formed, and the patterned light beam 26 is imaged by the projection system PS via the reflection elements 28, 30 to On the substrate W held by the wafer stage or the substrate table WT.

Each system IL and PS is configured in its own vacuum or near-vacuum environment, which is defined by an enclosure structure similar to the enclosure structure 220. More elements than those shown may generally be present in the lighting system IL and the projection system PS. In addition, there may be more mirrors than those shown in the figures. For example, in addition to the reflective elements shown in FIG. 2, there may be one to six additional reflective elements in the illumination system IL and / or the projection system PS. For example, the aforementioned U.S. patent application publication shows three additional elements in a lighting system.

Considering the source collector module SO in more detail, a laser energy source including a laser 223 is configured to deposit laser energy 224 to a material such as xenon (Xe), tin (Sn), or lithium (Li). In the fuel, a highly ionized plasma 210 having an electron temperature of tens of eV is generated. Other fuel materials such as Tb and Gd can be used to generate higher energy EUV radiation. The high-energy radiation generated during the plasma de-excitation and recombination is emitted from the plasma, collected by the near normal incidence collector mirror CO, and focused on the aperture 221. The plasma 210 and the aperture 221 are located at the first and second focal points of the collector or collector mirror CO, respectively.

In order to deliver fuel such as liquid tin, a droplet generator 226 is disposed in the enclosure 220, and the droplet generator 226 is configured to activate a high-frequency droplet stream 228 toward a desired portion of the plasma 210. In operation, laser energy 224 is delivered in synchronization with the operation of the droplet generator 226 to deliver a pulse of radiation to turn each fuel droplet into a plasma 210. Droplets can be delivered at several kilohertz, such as 50 kHz. In practice, laser energy 224 is delivered in at least two pulses: a pre-pulse and a main pulse. The pre-pulse delivers limited energy to the droplet before it reaches the plasma site, for example to shape the droplet for receiving the host by shaping the droplet into a cake or by vaporizing the fuel material into a small cloud. pulse. A main pulse is delivered to the conditioned droplets at the desired site to generate a plasma 210. The retainer 230 is disposed on the opposite side of the enclosure structure 220 to capture fuel that has not become a plasma for whatever reason.

In a typical lithography system, there are many additional components in the source collector module and the lithography device, but they are not shown here. These components include arrangements for reducing or mitigating the effects of contamination within the enclosed vacuum, such as to prevent deposits of fuel materials from damaging or impairing the performance of the collector mirror CO and other optics. Furthermore, one or more spectral purity filters may be included in the source collector module SO and / or the lighting system IL. In addition to EUV radiation of the desired wavelength, these filters are also used to eliminate as much of the unwanted wavelength radiation as possible from the laser and / or plasma 210. The spectral purity filter can be positioned near the virtual source point or at any point between the collector mirror CO and the virtual source point. The filter can be placed elsewhere in the radiation path, such as downstream of the virtual source point IF. Multiple filters can be deployed. Those skilled in the art are familiar with the need for such measures and the manner in which such measures can be implemented, and require no further details for the purposes of the present invention.

Referring to the laser 223 from FIG. 2 in more detail, the laser in the presented embodiment belongs to a Master Oscillator Power Amplifier (MOPA) type. This type consists of a "master" laser or "seed" laser labeled MO in the illustration, followed by a power amplifier (PA). A beam delivery system 240 is provided to deliver laser energy 224 into the module SO. In practice, the pre-pulse element of the laser energy will be delivered by a separate laser not shown separately in the diagram. The laser 223, the fuel source (ie, the droplet generator) 226, and other components may be controlled by the source control module 242, for example.

Those of ordinary skill will know that the reference axes X, Y, and Z can be defined to measure and describe the geometry and behavior of the lithography system, its various components, and the radiation beam 20, 21, 26. At each part of the lithography system, the local reference coordinate system of the X, Y, and Z axes can be defined. The Z axis is substantially coincident with the direction of the optical axis O at a given point in the system, and is substantially perpendicular to the plane of the patterned device (reduction mask) MA and the plane perpendicular to the substrate W. In the source collector module, the X-axis and the direction of the fuel stream (228, described below) are approximately coincident, and the Y-axis is orthogonal to that direction, which is indicated from the page, as indicated in Figure 2. On the other hand, in the vicinity of the support structure MT holding the reduction mask MA, the X axis is substantially transverse to the scanning direction aligned with the Y axis. For convenience, in this area of the schematic diagram of Figure 2, the X-axis is indicated from the page and again marked as such. These designations are well known in the art and will be used herein for convenience. In principle, any reference coordinate system can be selected to describe the lithographic system and its behavior.

Referring to the lighting system in more detail, the faceted scene mirror device 22 includes an array of individual facets, so that the EUV radiation beam 20 is divided into several sub-beams, one of which is labeled 260 in the diagram. Each sub-beam is directed to an individual facet on the faceted pupil mirror device 24. The facet of the pupil mirror device 24 is configured to direct its individual sub-beams to a target that is a slot-shaped region of the patterned device MA. When the illumination arriving from the source collector module is highly non-uniform in its angular distribution, the sub-beams 260 and the single beam 21 combined are designed to generate highly uniform illumination throughout the gap area. It is also known that the facets of the devices 22 and / or 24 may be steerable and / or obscurable in order to implement different lighting modes.
The conditioned EUV radiation beam 21 is delivered to the patterning device MA via the conditioning and shielding module 262. This module includes a shading unit, also known as a reduction mask (REMA), which can have movable blades that define a range of illumination gaps in the X and Y directions. Generally, the lighting gap as applied in an EUV-type lithographic apparatus may be curved.
In front of the REMA, there is also a Uniform Lighting Correction Module (UNICOM).

In order to expose the target portion C on the substrate W, a radiation pulse is generated on the substrate table WT, and synchronous movements 266, 268 are performed via the shadow table MT to scan the pattern on the patterning device MA through the illumination gap.

Examples of lighting systems including REMA and UNICOM functions are described in US Patent Application Publication Nos. 2005 / 0274897A1 and 2011 / 0063598A.

Many measures are applied in the source controller 242. Such measures include monitoring to ensure that the virtual source point IF is aligned with the aperture 221 at the exit of the source collector module SO. In systems based on LPP sources, alignment control is usually achieved by controlling the location of the plasma 210 rather than by moving the collector mirror CO. The collector mirror, exit aperture 221, and illuminator IL are accurately aligned during the setup procedure so that the aperture 221 is located at the second focus of the collector mirror. However, the exact location of the virtual source point IF formed by the EUV radiation at the exit of the source optics depends on the exact location of the plasma 210 relative to the first focus of the collector mirror. Fixing this location accurately enough to maintain sufficient alignment often requires active monitoring and control.

For this purpose, the source control module (controller) 242 controls the position of the plasma 210 (the EUV radiation source) in this example by controlling the injection of fuel and also controlling the timing of, for example, the application of energy to pulses from the laser. . In a typical example, the energy pulses of the laser radiation 224 are delivered at a rate of 50 kHz (period 20 μs) and in bursts that last any time, such as 20 ms to 20 seconds. The duration of each main laser pulse can be about 1 μs, and the resulting EUV radiation pulse can last about 2 μs. With proper control, it is considered that the EUV radiation beam is accurately focused on the aperture 221 by the collector mirror CO. If this is not achieved, all or part of the beam will be irradiated on the surrounding material of the enclosure structure.

The source control module 242 is supplied with monitoring data from one or more sensor arrays (not shown), which sensors provide a first feedback path for information about the location of the plasma. The sensors may be of various types, such as described in US Patent Application Publication No. 2005 / 0274897A1 mentioned above. The sensor may be located at more than one location along the radiation beam path. For example only, the sensors may be located around and / or behind the scene mirror device 22, for example. The sensor signals just described can be used to control the illuminator IL and the optical system of the projection system PS. Through the feedback path, these sensor signals can also be used to assist the control module 242 of the source collector module SO to adjust the intensity and position of the EUV plasma source 210. The sensor signal can be processed, for example, to determine the observation site of the virtual source IF, and extrapolate this site to indirectly determine the site of the EUV source. If the virtual source part drifts, as indicated by the sensor signal, a correction is applied by the control module 242 to re-center the beam in the aperture 221.

The additional sensors and feedback paths can usually be set in the source collector module SO itself, rather than relying entirely on the signals from the illuminator sensors to achieve faster, direct and / or independent control of the radiation source . Such sensors may include, for example, one or more cameras that monitor the location of the plasma. In this way, the partial beam 20 is maintained in the aperture 221, and damage to the equipment is avoided and efficient use of radiation is maintained.

To ensure that the substrate W is provided with an appropriate dose of radiation, it is important to ensure that the collector or collector mirror CO adequately reflects the EUV radiation generated. In detail, it is necessary to make the collector mirror CO have a sufficiently high reflectance, and it is necessary to make the reflectance as uniform as possible.

In this regard, it may be pointed out that during the generation of EUV radiation as described above, debris may be generated due to the interaction of the fuel droplet stream 228 and the laser pulse. Such debris may cause contamination of the collector mirror CO, thus adversely affecting reflectance and reflectance uniformity. In addition, other sources of debris may adversely affect the reflectance and reflectance uniformity of the collector mirror CO. Possible sources of such contamination include, for example, droplets or particles or contaminants falling from components of the EUV source disposed above the collector mirror CO, or contamination due to jets such as the surface of the bucket or the surface of a tin trap.

To reduce the adverse effects of pollution, collector mirrors such as the collector mirror CO shown in FIG. 2 may be subjected to a cleaning procedure to remove the pollution. Such cleaning procedures may include, for example, carbon dioxide snow cleaning procedures.

In order to check that the cleaning procedure has been effective, it is preferable to subject the collector mirror to a test after the cleaning procedure, whereby the reflectance of the face mirror is evaluated, for example, at a plurality of locations on the collector mirror.

The present invention provides a system for performing such detection or testing of a collector mirror of an EUV lithography system, and a method of detecting or testing a collector mirror of an EUV lithography system.

More generally, the present invention provides a system for performing inspection or testing of a mirror. The invention can be used to detect or test various types of masks. Examples of such mirrors include mirrors such as those used in EUV radiation sources, lithographic projection systems, lighting systems as used in lithographic devices, and the like. Referring to FIG. 2, the present invention may be applied to detect or test a collector mirror CO, as used in the illuminator IL, for example, any one of the field facet device 22 or pupil facet device 24, as used in the projection system PS Any mirror such as a reflective element 28 or 30 is applied.

Fig. 3 schematically shows an embodiment of a system according to the invention for testing a collector mirror. The collector mirror 300 has a first focus / focal point 310 and a second focus 320. The focus 310 may, for example, substantially correspond to a portion where the radiation emitting plasma 210 is formed as shown in FIG. 2, and the focus 320 may correspond to, for example, an intermediate focus IF as shown in FIG. 2.

The system according to the present invention includes a test radiation subsystem 330 operable to project test radiation 330.1 from the second focus 320 onto the collector mirror 300. Within the meaning of the present invention, test radiation refers to radiation used during testing or detection of a mirror, such as the collector mirror 300 shown.
In one embodiment of the invention, the test radiation as applied has a wavelength or wavelength spectrum selected based on the radiation used under normal operating conditions of the collector mirror. In detail, if the collector mirror is to be used in an EUV lithography system, the wavelength or wavelength spectrum of the test radiation can be selected based on the EUV radiation applied to the lithography device. Thus, in one embodiment of the present invention, the test radiation may include radiation having a wavelength in a range of 10 nm to 20 nm. In one embodiment, the applied test radiation may have a wavelength spectrum of 13.5 nm +/- 1 nm, FWHM-full width at half maximum. In one embodiment, the test radiation subsystem as applied in the system according to the present invention may be configured to apply radiation of different wavelengths or different wavelength ranges to detect or test the mirror. In such embodiments, the test radiation subsystem may include multiple radiation sources and / or multiple filters, which are used to filter the generated radiation in order to achieve the desired test radiation. As an example, it may be useful to evaluate the reflectance of a mirror such as the collector mirror 300 at different wavelengths or wavelength ranges. It may be useful, for example, to evaluate the reflectance of the collector mirror in the aforementioned spectrum of 13.5 nm +/- 1 nm and in a spectrum that encompasses or includes infrared (IR) radiation.
In an embodiment, the test radiation subsystem is configured to generate test radiation across an angle α ₀ so that the entire collector mirror 300 can be irradiated in principle. Please note that the diagram of FIG. 3 represents the collector mirror 300 in a two-dimensional cross section, and in practice, test radiation is typically emitted in three dimensions. Therefore, when the three-dimensional test radiation pattern is projected onto a two-dimensional plane having a cross-section of the collector mirror 300, the angle α ₀ in FIG. 3 is the angle from which the three-dimensional test radiation pattern opposes. In one embodiment, the test radiation subsystem is configured to generate test radiation that spans an angle less than the angle α ₀ . In such embodiments, the entire collector mirror 300 may still be scanned or irradiated, for example, by rotating the test radiation subsystem 330 or a portion thereof.

The system according to the invention further comprises a sensor subsystem, indicated schematically by the element symbol 340, the sensor subsystem being operable to receive test radiation reflected from the collector mirror 300 towards the first focus 310, for example by arrow 342 Indicated test radiation. In an embodiment, as will be discussed in more detail below, the sensor subsystem 340 may include one or more of the test radiation reflected from the mirror--that is, the collector mirror 300-- Sensor or detector.

According to the present invention, the system for testing a collector mirror further includes a radiation limiter subsystem 360. The radiation limiter subsystem 360 is configured to limit the test radiation as received by the sensor subsystem 340 to test radiation reflected from a restricted portion of the collector mirror 300. Thus, the radiation measured or detected by the sensor subsystem will only involve radiation reflected from a restricted portion of the collector mirror 300. In the embodiment as shown, the restricted portion of the collector mirror is indicated by the mirror segment 300.1. By limiting the test radiation as received by the sensor subsystem to test radiation reflected from a restricted portion of the collector mirror, we can evaluate the effectiveness of that particular part of the collector mirror, such as evaluating the reflectance of that part .

In the embodiment as shown, the radiation limiter subsystem 360 is configured to pass only a small portion of the generated radiation 330.1 toward the collector mirror. A small part of the radiation 330.1 opposes an angle much smaller than the angle α ₀ . In order to achieve that situation, the radiation limiter subsystem 360 includes a shielding member 360.1 that blocks the test radiation, whereby the shielding member 360.1 includes a small aperture through which a small portion of the test radiation 330.1 can pass, such as a tubular aperture 360.2. The radiation limiter subsystem 360 thus enables only restricted portions, such as the portion 300.1 of the collector mirror 300, to be irradiated by the test radiation generated by the test radiation subsystem 330.

According to the invention, the system further includes a control subsystem 370 configured to control the movement of the radiation limiter subsystem 360, for example, by providing a control signal 370.1 to the radiation limiter subsystem 360. In detail, the control subsystem 370 is configured to control the position of the radiation limiter subsystem 360 so that the restricted portion of the collector mirror irradiated by the test radiation can be changed. Thus, the control subsystem may, for example, be configured to control the movement of the radiation limiter subsystem along a series of different positions, thereby limiting the test radiation as received by the sensor subsystem 340 to the collector mirror 300. A series of test radiation reflected by different restricted sections. In this way, the effectiveness of different restricted parts of the collector mirror can be evaluated, such as the reflectance of these parts.

In one embodiment of the invention, a set of different restricted portions substantially covers the entire collector mirror 300.

In one embodiment of the invention, the radiation limiter subsystem includes one or more actuators to displace the aperture tube 360.2, for example, along with the shielding member 360.1, in order to change the restriction of the collector mirror 300 irradiated by the test radiation section. In such embodiments, the aperture tube 360.2 may be rotated, for example, about an axis that is perpendicular to the drawing plane and, for example, through the second focal point 320. Thereby, the angle α which defines the angle at which the test radiation is irradiated on the collector mirror can be modified. In a similar manner, the aperture tube 360.2 can be rotated, for example, about an axis parallel to the indicated Z-axis and, for example, through the second focal point 320. By combining the two rotational movements, the entire surface of the collector mirror can be selectively scanned by the test radiation. This embodiment is explained in more detail below.

Those skilled in the art will understand that other types of actuators, such as linear actuators or motors, can also be used to displace the radiation limiter subsystem, thereby controlling which restricted portion of the collector mirror is being irradiated .

In one embodiment of the invention, the test radiation subsystem 330 or the radiation limiter subsystem 360 is configured to shape the generated test radiation into a light beam. In such embodiments, the test radiation subsystem 330 and / or the radiation limiter subsystem 360 are configured to project the test radiation as a light beam onto the collector mirror 300. In such embodiments, the control subsystem 370 may be configured to direct the beam or beam-shaping test radiation to a plurality of different restricted portions of the collector mirror, one restricted portion followed by another restricted portion. guide. Such sequential projection of the test radiation beam onto different restricted parts of the collector mirror may also be referred to as scanning the collector mirror with the test radiation beam. During such a scanning procedure by which a portion of the collector mirror 300 or the entire mirror is scanned, the sensor subsystem 340 may generate a set of measurement data representing test radiation reflected from different restricted portions of the collector mirror 300. Such measurement data may be provided to the control subsystem 370 of the system according to the invention, for example via a data channel, as indicated by arrow 370.2. In one embodiment, the received measurement data 370.2 may be processed by the processing unit 380 of the control subsystem 370, for example. Such a processing unit may be embodied, for example, as a processor, a microprocessor, a computer, or the like. Such a processing unit 380 may include, for example, a memory unit for storing measurement data.

In an embodiment, the processing unit 380 may be configured to process the measurement data in order to determine a spatial reflectance distribution of at least a portion of the collector mirror. In such embodiments, the measurement data representing the test radiation reflected from different restricted portions of the collector mirror 300 and the data representing the test radiation generated or emitted may be compared to determine the different restricted portions of the collector mirror Of reflectance. An example of a measure of reflectance is the ratio of the amount of test radiation received to the amount of test radiation generated or emitted, and the amount of test radiation generated or emitted on the one hand and the amount of test radiation received on the other The difference. Therefore, in one embodiment of the present invention, the measurement data obtained from the sensor subsystem 340 can be supplemented with active measurement data, and the source measurement data represents the amount of test radiation emitted or generated during the scanning procedure. Such source measurement data may be provided to the processing unit 380 of the control subsystem 370, for example, via a data channel, as indicated by arrow 370.3. In such embodiments, the test radiation subsystem 330 may also include a sensor called a source sensor, which is configured to generate a source quantity that represents the test radiation projected by the test radiation subsystem 330测 信号。 Test signal. By combining the measurement data of the sensor subsystem and the source measurement data of the test radiation subsystem, the reflectance across the collector mirror 300 can be more accurately evaluated, because the source measurement data can be considered as in Any fluctuations in test radiation generated and emitted during the scanning procedure.

As an alternative to applying a source sensor in the test radiation subsystem 330, it is worth mentioning that the sensor can also be applied to the aperture tube 360.2 in order to obtain the amount of test radiation emitted towards the collector mirror 300 Measure. In a similar manner, the measurement data of such an aperture sensor and the measurement data obtained from the sensor of the sensor subsystem 340 can be combined to determine the spatial reflectance map of at least part of the collector mirror 300.

Preferably, as already indicated above, for example when the collector mirror is used in a lithography system as illustrated in FIG. 2, the wavelength or wavelength spectrum of the applied test radiation preferably corresponds to that of the collector The wavelength or wavelength spectrum used during normal operation of the mirror. With this, we can more accurately determine the reflectance of the collector mirror for the relevant wavelength or wavelength spectrum. To achieve this, there are different options.
In one embodiment of the present invention, the test radiation subsystem 330 includes a radiation source and a multi-layer mirror assembly, and the multi-layer mirror assembly is used to spectrally filter the generated radiation in order to achieve the required test radiation, that is, to have Test radiation of appropriate wavelength or wavelength spectrum. As is known, a multi-layered mirror, also called a Bragg mirror, is a type of reflective optical element composed of multiple layers having alternating thicknesses and refractive indices. The thickness is tuned to control constructive interference of radiation of the desired wavelength reflected from subsequent layers. In one embodiment, the radiation source of the test radiation subsystem 330 includes a Xe EUV source. In such embodiments, the multi-layered mirror configuration may be configured to filter radiation into a wavelength spectrum of, for example, 13.5 nm +/- 1 nm, FWHM-full width at half maximum.

FIG. 4 schematically shows three possible multi-layer mirror configurations for generating appropriate test radiation, which test radiation may be applied, for example, in a test radiation subsystem 330 of a system according to the present invention.

Fig. 4a schematically shows a radiation source 420, such as a radiation source for generating EUV radiation. In the embodiment as shown, the aperture 410 is provided to allow a portion of the generated radiation indicated by the arrow 420.1 to shine on the first mirror 430, such as a multi-layer mirror. The first mirror 430 is configured to reflect the received radiation toward a second mirror 440, such as a multi-layer mirror, as indicated by arrow 420.2. The second mirror 440 is configured to reflect the received radiation toward the aperture 450, as indicated by arrow 420.3. The aperture may be, for example, an outlet of an aperture tube 460 configured to receive radiation 420.3 reflected from the mirror 440. In the embodiment as shown, the mirrors 430 and 440 may be used to filter inappropriate wavelengths or wavelength components from the radiation as generated by the source 420. Alternatively or in addition, the mirrors 430 and 440 may form a beam expander or a beam compressor for controlling the width of a light beam formed by the test radiation irradiated on the collector 300 and thus the intensity of the light beam.

In one embodiment of the present invention, the mirror assembly includes the mirrors 430 and 440, and the aperture tube 460 may serve as a radiation limiter subsystem as discussed above. In such embodiments, the mirror assembly and aperture tube can be configured, for example, to be displaceable relative to the radiation source 420 in order to change the orientation of the radiation 420.3 emitted from the aperture. By appropriately sizing the mirror or mirror assembly, the radiation beam 420.3 emitted from the aperture 450 can be a collimated beam 420.4, that is, a parallel radiation beam that can be irradiated on a restricted portion of the collector mirror. In order for the collimated light beam 420.4 to be reflected from the collector mirror toward the first focus of the mirror, the collimated light beam 420.4 needs to be emitted from the second focus. This can be achieved, for example, by configuring the mirror assembly and the aperture tube so that the second focus is inside the aperture tube, for example, at the location 470.

Figure 4b schematically illustrates another embodiment of a mirror assembly that can be applied to filter radiation from a radiation source. Fig. 4b schematically shows a radiation source 520, such as a radiation source for generating EUV radiation. In the embodiment as shown, the radiation source 520 is configured to emit a portion of the generated radiation indicated by arrow 520.1 to illuminate a first mirror 530, such as a multi-layer mirror, shown here in cross section. The first mirror 530 is configured to reflect the received radiation toward a second mirror 540, such as a multi-layer mirror, as indicated by arrow 520.2. The second mirror 540 is configured to reflect the received radiation toward a focal point 550. As discussed above, the mirrors 530 and 540 can be used to filter the radiation as generated by the radiation source 520 to obtain test radiation having an appropriate wavelength or spectrum. Forward from the focal point 550, the filtered radiation 520.3 can be used as test radiation for, for example, scanning a collector mirror as discussed above with reference to FIG. In such embodiments, the generated test radiation may be limited by, for example, a radiation limiter 360 configured to limit the generated test radiation, such as radiation 520.3, to irradiate a restricted portion of the collector mirror. In order to ensure that the emitted test radiation 520.3 or a portion of it irradiated on the collector mirror reflects from the collector mirror, such as the collector mirror 300, toward the first focus of the mirror, a second focus emission test is required Radiation 520.3. This can be achieved, for example, by configuring the mirror assemblies 530, 540 so that the second focus of the collector mirror and the focus 550 substantially coincide.

The mirror configuration including the mirrors 530 and 540 is called a Schwarzschild objective lens.

FIG. 4c schematically shows another embodiment of a mirror assembly that can be applied to filter radiation from a radiation source. The mirror assembly also includes Schwartzchild objective lenses including mirrors 630 and 640. . Fig. 4c schematically shows a radiation source 620, such as a radiation source for generating EUV radiation. In the embodiment as shown, the radiation source 620 is configured to emit a portion of the generated radiation indicated by arrow 620.1 to illuminate a first mirror 630, such as a multi-layer mirror, shown here in cross section. The first mirror 630 is configured to reflect the received radiation toward a second mirror 640, such as a multi-layer mirror, as indicated by arrow 620.2. The second mirror 640 is configured to reflect the received radiation through the aperture 660 of the first mirror 630 as a collimated beam 620.3. Those skilled in the art will understand that by properly sizing and positioning the facets 630 and 640 of the Schwarzschild objective lens, we can ensure that the emitted radiation is shaped into a collimated beam 620.3 instead of as shown in the figure. Focus on focus 550 as shown in 4b. In such configurations, the mirror configurations 630, 640 can therefore both act as filters for test radiation generated with an appropriate wavelength or wavelength spectrum, and shape the test radiation to obtain a configuration to illuminate the detected Test radiation beam 620.3 on a restricted portion of the collector mirror. Thus, the mirror configuration can be viewed as acting as a radiation limiter, which limits the test radiation to shine on the restricted portion of the collector mirror.
Again, in order to ensure that radiation is reflected from the collector mirror, such as collector mirror 300, toward the first focus of the face mirror, test radiation 620.3 needs to be emitted from the second focus of the collector mirror. This can be achieved, for example, by arranging a second mirror 640 at or near the second focus of the inspected collector mirror.
In a similar manner as discussed above, the multi-layered mirror assembly 630, 640 may be configured to be displaceable to scan at least a portion of the surface of the collector mirror with test radiation 620.3 in order to determine the reflectivity of the mirror.

In one embodiment of the invention, the test radiation subsystem as applied further comprises a sensor for sensing radiation as emitted by the source. Such sensors, also referred to as source sensors, may be configured, for example, to directly receive radiation as emitted by the source. In Figure 4c, such a sensor 650 is shown schematically, the sensor 650 being configured to receive radiation 620.4 as emitted by the source 620. Alternatively, the source sensor 650 may be configured to receive reflected test radiation from a mirror, such as a first mirror 630 or a second mirror 640, used in a mirror configuration as applied in one embodiment of the present invention. Part of it. In such a configuration, the source sensor can therefore measure radiation having the same wavelength or wavelength spectrum as the test radiation as received by the collector mirror.

In one embodiment of the present invention, a source sensor, that is, a sensor configured to generate source measurement data representing radiation emitted by a source of a test radiation subsystem or a source of test radiation may also be configured at In a radiation limiter subsystem such as the radiation limiter subsystem 360 shown in FIG. 3. In such embodiments, the source sensor may be configured at or near or in the aperture tube 360.2 of the radiation limiter subsystem 360 to capture a portion of the radiation irradiated by the test radiation subsystem 330.

As has been indicated above, the system according to the present invention includes a sensor subsystem, such as the sensor subsystem 340 shown in FIG. 3. Various embodiments of such a sensor subsystem as applied in the present invention are discussed in FIG. 5.

Fig. 5a schematically shows a first configuration of a sensor subsystem 700 as applicable in a system according to the invention, and a collector mirror 300 whose reflectance is to be checked. The sensor subsystem 700 includes a sensor 700.1 having an active area 700.2 facing the collector mirror 300. In the embodiment as shown, the active area 700.2 is considered to be located at or near the first focus of the collector mirror 300 to receive test radiation emitted from the second focus and then reflected from the mirror 300.
In an embodiment, the sensor 700.1 may include, for example, an EUV photodiode. The sensor subsystem 700 further includes an output 700.3 for outputting a measurement signal 700.4 representing the received radiation.

In the configuration as shown, the sensor subsystem is configured to remain stationary relative to the collector mirror 300. Therefore, depending on the angle of the emitted radiation, the incident angle of the test radiation reflected from the collector mirror 300 may vary with respect to the optical axis O, as shown by the light beams 710.1 and 710.2. With calibration, the effect of the angle of incidence on the received radiation can be considered.

As an alternative, as shown schematically in FIG. 5b, a sensor subsystem 750 may be applied, which includes a plurality of sensors 750.1, 750.2, and 750.3 with different orientations with respect to the optical axis O. Therefore, depending on the incident angle of the received radiation, we can choose the most sensitive sensor, that is, the sensor that best faces the received radiation in the active area.

Fig. 5c schematically shows yet another alternative sensor subsystem 760 and a collector mirror 300, which includes a sensor 760.1 with an active area 760.2. The sensor subsystem further includes an actuator or actuator configuration 770 configured to displace the sensor 760.1 relative to the optical axis O. In detail, the actuator configuration may be configured to rotate the sensor 760.1 about an axis 780 and about an axis that is perpendicular to the drawing and intersects the first focus of the collector mirror, the axis 780 being parallel to the indicated Z direction and Intersects the first focus of the collector mirror. In such a configuration, the sensor 760.1, especially the active area 760.2 of the sensor 760.1, may be directed to face the test radiation that is reflected toward the first focus, such as the reflected light beam that faces the radiation beam 710.2.

In an embodiment, as shown schematically in FIG. 5d, the sensor 790.1 of the sensor subsystem 790 as applied in a system according to the present invention may be installed inside a tube, such as inside an aperture tube 795. In the embodiment as shown, the sensor 790.1 and the aperture tube 795 can be displaced by an actuator or actuator arrangement 770 as discussed above, so as to face reflections from the collector mirror, such as facing the radiation beam 710.2 The reflected beam. By disposing the sensor 790.1 inside or at the distal end of the aperture tube 795, the sensor 790.1 can only sense the radiation received by the aperture tube 795. Thereby, the measurement disturbance due to stray radiation can be reduced or avoided.

The sensor subsystem as shown schematically in Figs. 5a to 5d is configured to directly receive reflected radiation, that is, no spectral filtering of reflected radiation is applied. As discussed above, it may be preferable to use a test radiation having a wavelength that is the same or similar to the wavelength applied during normal operation to detect or test the collector mirror, because I am particularly interested in characterizing it for that particular wavelength. Or the collector spectrum of the wavelength spectrum is of interest. In order to perform such an evaluation using the sensor subsystem of Figs. 5a to 5d, it may be advantageous to combine a test radiation subsystem configured to filter test radiation-such as depicted in Figs. 4a to 4c The test radiation subsystem shown below-and these systems are used in which a first mirror and / or a second mirror can be implemented using a spectral purity filter.

Regardless of whether the test radiation subsystem applies the test radiation filter, we can apply the test radiation filter reflected from the collector mirror in a similar manner. Such embodiments are shown schematically in Figures 5e to 5f.

Fig. 5e schematically shows a sensor subsystem 800 and a collector mirror 300 as applicable in a system according to the invention. The sensor subsystem 800 as shown schematically includes a sensor 800.1, and the multi-layered mirror assembly includes a pair of mirrors 810, 820 configured to collect self-collection according to the indicated arrow 830.2 The test radiation 830.1 reflected by the mirror 300 is reflected toward the sensor 800.1. In the embodiment as shown, the incident radiation 830.1 is received by the aperture tube 840, which is configured to receive the reflected radiation toward the first focus 850 of the collector mirror 300. In one embodiment of the present invention, the sensor subsystem 800 may be further equipped with an actuator or an actuator configuration configured to adjust the aperture tube, the multi-layer mirror assembly, and the sensing device. At least one of the collectors in order to receive radiation reflected from different restricted portions of the collector mirror.

In one embodiment of the present invention, the sensor subsystem as applied in a system according to the present invention may use Schwarzschild objectives to test any incident radiation--that is, the reflection from the collector mirror 300 Radiation--Spectral filtering. Such an embodiment is shown schematically in Figure 5f. Fig. 5f schematically shows a sensor subsystem 900, as well as a collector mirror 300, as applicable in a system according to the invention. The sensor subsystem 900 as shown schematically includes a sensor 900.1, and the multi-layered mirror assembly includes a pair of mirrors 910, 920 shown in cross-section, the mirrors 910, 920 being configured to indicate The arrow 930.2 reflects the test radiation 930.1 reflected from the collector mirror 300 toward the sensor 900.1. It can be seen that the mirrors 910 and 920 form Schwarzschild objectives, which are configured to receive the test radiation beam 930.1 reflected from the collector mirror 300 toward the first focus of the collector mirror. In an embodiment as shown, the first focus of the collector mirror may, for example, be configured to substantially coincide with the first mirror 910. In the embodiment as shown, the incident radiation 930.1 is received via an aperture tube 940 configured to receive the reflected radiation towards the first focus of the collector mirror 300, that is, where the mirror 910 is positioned Receive reflected radiation. In one embodiment of the present invention, the sensor subsystem 900 may be further equipped with an actuator or an actuator configuration configured to adjust the aperture tube, the multi-layer mirror assembly, and the sensing device. At least one of the filters in order to receive radiation reflected from different restricted portions of the collector mirror 300. It may be noted that the mirror configurations 910, 920 may be configured in a similar manner to the mirror configuration shown in FIG. 4c, but used in the opposite way; that is, in the embodiment of FIG. The German objective is used to generate a collimated beam from a radiation source, and in the embodiment of FIG. 5f, the Schwarzschild objective is configured to receive the collimated beam 930.1 and project it onto the sensor.

In the embodiment of the sensor subsystem shown in FIG. 5e or 5f, a mirror configuration is used to filter the test radiation as received by the sensor. When using such embodiments, filtering of the radiation generated by the source may be omitted.

In the configuration shown in FIG. 3, the radiation limiter subsystem 360 is configured in the beam path between the test radiation subsystem 330 and the collector mirror 300. Thus, only the restricted portion 300.1 of the collector mirror 300 is irradiated at a time. Alternatively, the radiation limiter subsystem may be implemented in a radiation path between the collector mirror 300 and the sensor subsystem 340. In such embodiments, the test radiation emitted toward the collector mirror 300 need not be spatially limited to illuminate only a restricted portion of the collector mirror, because the limitation of the test radiation as received by the sensor is limited The radiation limiter subsystem in the radiation path between the collector mirror 300 and the sensor subsystem 340 is restricted. In an embodiment of the present invention, the radiation limiter subsystem includes a first radiation limiter subsystem configured in a path between the test radiation subsystem and the collector mirror, and the collector mirror and the sensor subsystem. A second radiation limiter subsystem in the path between the systems. In such a radiation limiter subsystem, the first radiation limiter subsystem may include, for example, a first shielding member having a first aperture in the first shielding member, and the first shielding member is disposed between the second focus and the collector mirror. The second radiation limiter subsystem may include, for example, a second shielding member having a second aperture in the second shielding member, and the second shielding member is disposed between the collector mirror and the first focus. Between the test radiation in the optical path. It should be noted that within the meaning of the present invention, an optical path may refer to a trajectory followed by test radiation, even though the applied radiation may not be visible.

Such an embodiment is shown schematically in FIG. 6. FIG. 6 schematically shows the same features and components as FIG. 3. In addition, this embodiment includes another radiation limiter subsystem 390 that is configured to limit the test radiation as received by the sensor subsystem 340 to the radiation from the collector mirror 300. Limits the radiation reflected by 300.1. In the embodiment as shown, another radiation limiter subsystem 390 includes a shielding member 390.1 protruding from the aperture tube 390.2. Since the radiation limiter subsystem is included in both the optical path between the collector mirror and the first focus and the optical path between the second focus and the collector mirror, stray light effects can be reduced or avoided. Those skilled in the art will understand that the displacements of the two radiation limiter subsystems are synchronized because the two radiation limiter subsystems need to be oriented toward the same restricted portion, such as the portion 300.1 of the collector mirror 300.

In one embodiment of the present invention, the radiation limiter subsystem includes a hemispherical shielding member and an aperture tube protruding through the apex of the hemisphere. Such an embodiment is shown schematically in FIG. 7. FIG. 7 schematically shows a radiation limiter subsystem including a hemispherical shielding member 950 and an aperture tube 960 protruding through the apex of the hemisphere. The radiation limiter subsystem further includes an actuator configuration 970 including a first actuator 970.1 configured to rotate the shielding member 950 and the aperture tube 960 about an axis parallel to the indicated X axis, and A second actuator 970.2 configured to rotate the shielding member 950 and the aperture tube 960 about an axis parallel to the indicated Z axis. The radiation limiter subsystem as shown schematically in FIG. 7 may be applied, for example, as the radiation limiter subsystem 360 shown in FIG. 6, the radiation limiter subsystem 390 shown in FIG. 6, or both. The actuator assembly 970, as shown schematically, may also be used to displace any of the test radiation subsystems shown in Figs. 4a to 4c, and / or to move the Any one of the sensor subsystems is displaced.

In one embodiment of the present invention, a radiation limiter subsystem as schematically shown in FIG. 7 is applied, so that a part of the center 975 of a sphere formed by a hemisphere substantially corresponds to the position of the first focus or the second focus .

It may be advantageous to calibrate the system before a mirror such as the collector mirror 300 is detected or tested by the system according to the present invention. In one embodiment of the present invention, a calibration method is proposed to emit test radiation emitted by the test radiation subsystem directly toward the sensor subsystem. Fig. 8 schematically shows a system according to the invention arranged in a calibration position. The system shown schematically corresponds substantially to the system shown in FIG. 6, and the system includes a test radiation subsystem 330, a sensor subsystem 340, a control subsystem 370, and a radiation limiter subsystem. The radiation limiter The subsystem includes a first radiation limiter subsystem 360 and a second or another radiation limiter subsystem 390. In contrast to the situation as depicted in FIG. 6, the radiation limiter subsystems 360 and 390 as shown in FIG. 8 are configured—that is, rotated— such that the apertures 360.2 and 390.2 point toward each other. In such a position, which is also referred to as a calibration position, the test radiation beam 1000 can be directly transmitted through the aperture 360.2 into the aperture 390.2 for reception by the sensor subsystem 340, and in particular by the sensor subsystem 340. Tester receives. We can calibrate the system by comparing the source measurement data in the calibration position--that is, the data indicating the amount of radiation emitted by the test radiation subsystem 330--and the measurement data obtained from the sensor subsystem 340. That is, the relationship between the emitted test radiation and the received test radiation is determined in the absence of a collector mirror. In FIG. 8, the component symbols 370.2 and 370.3 may indicate the obtained measurement data and source measurement data as provided to the control unit 370, respectively. In one embodiment of the present invention, before determining the measurement or test sequence of the reflectance of the collector mirror, a ratio of the amount of received radiation to the amount of emitted radiation, or the amount of received radiation to the emitted light may be determined. The difference between the amount of radiation.
In one embodiment of the present invention, after the measurement or test sequence of the reflectance of the collector mirror is determined, the ratio of the received radiation to the emitted radiation, or the difference may be determined again. By determining the mentioned ratio or difference before and after the measurement sequence, any drift or degradation of the test radiation subsystem 330 or the sensor subsystem 340 can be detected and considered.

Regarding the calibration method as discussed, it can be pointed out that the same method can also be applied when the first radiation limiter subsystem 360 or the second radiation limiter subsystem 390 is omitted.

In one embodiment of the present invention, a mask, such as a collector mirror 300, is mounted at a substantially stationary frame during a test or test.

In one embodiment of the invention, during normal operation, the mirror is mounted at such a frame in an orientation relative to gravity that substantially corresponds to the orientation of the mirror to be detected or tested. Such an embodiment is shown schematically in FIG. 9 for a collector mirror 1100.

FIG. 9 schematically illustrates a collector mirror 1100 installed inside the system 1200 according to an embodiment of the present invention. In the embodiment as shown, the system includes a first vacuum chamber or container 1210 in which the collector mirror 1100 may be configured on, for example, a frame 1220. In the embodiment as shown, the container 1210 is mounted to the outer frame 1230 at an angle selected, for example, such that the collector mirror 1100, when mounted to the frame 1220, is substantially the same as the angle applied during normal operation Angle configuration. By this, we can assume that any deformation of the collector mirror 1100, such as due to gravity, will substantially correspond to that of the mirror 1100 during normal operation--that is, for example, when installed on a system such as that shown in FIG. The distortion of the EUV source in the shadow system. The system 1200 further includes a test radiation subsystem 1240 configured to emit test radiation 1240.1 from a second focus 1250 of the collector mirror, and a test configured to receive reflection from the collector mirror 1100 toward the first focus 1255 of the collector mirror 1100 The sensor subsystem 1260 radiating 1260.1. In the embodiment as shown, in a similar manner as shown in FIG. 6, the system 1200 further includes a radiation limiter subsystem including a first radiation limiter subsystem 1270 and a second or another Radiation limiter subsystem 1280, which is configured to limit the test radiation as received by the sensor to test radiation reflected from a restricted portion of the collector mirror 1100. Arrow 1285 schematically illustrates the possible displacement of the radiation limiter subsystems 1270 and 1280 during the test of the collector mirror. In the embodiment as shown, the first radiation limiter subsystem 1270 includes a shielding member 1270.1 and an aperture tube 1270.2. In the embodiment as shown, the test radiation subsystem 1240 is configured in a second vacuum chamber or container 1290. The first vacuum chamber 1210 and the second vacuum chamber 1290 are separated by a wall 1300, which contains a pair of substantially The upper parallel wall portions 1300.1 and 1300.2 have apertures in the wall portions 1300.1 and 1300.2 to allow test radiation to pass towards the collector mirror. In the embodiment as shown, the wall portions 1300.1 and 1300.2 are separated up to a gap 1310, which is configured to receive the shielding member 1270.1 of the first radiation limiter subsystem 1270. In the embodiment as shown, the aperture in the wall 1300 is configured so that the test radiation as emitted can reach all parts of the collector mirror 1100. By disposing the shielding member 1270.1 of the first radiation limiter subsystem between the two wall portions 1300.1 and 1300.2 separating the walls of both the vacuum chambers 1210 and 1290, a labyrinth will be generated, which will block or hinder the Any debris generated by the test radiation subsystem 1240 propagates into a vacuum chamber 1210 containing a collector mirror. To further obstruct or block the contamination of the vacuum chamber 1210, the system according to the present invention may further include a purge gas subsystem configured to introduce a purge gas stream toward the second vacuum chamber 1290 in order to hinder the propagation of debris To the first vacuum chamber 1210. The component symbol 1320 refers to such a purge gas subsystem. It can also be pointed out that the purge gas subsystem can be used to purify any of the aperture tubes used in embodiments of the present invention in order to prevent debris from propagating towards the collector mirror.

As already discussed above, in one embodiment of the present invention, a system for detecting or testing a collector mirror, such as a collector mirror of an EUV radiation source, is configured to be exposed to test radiation, such as a test radiation beam- -Restricted part of the radiation collector mirror. In other words, the test radiation subsystem as applied in the system according to the present invention can be configured to irradiate the light spot on the collector mirror, and the size of the irradiated light spot corresponds to the size of the radiation beam, that is, as The size of the applied test radiation beam. In principle, the size of the applied light spot can be selected randomly. Those skilled in the art will understand that the smaller the light spot size--that is, the restricted portion corresponding to the measurement of the collector mirror radiation per measurement--the smaller the higher the resolution of the obtained reflectance map. . In addition, the smaller the spot size, the longer the measurement that can be taken by the entire collector mirror, and the smaller the signal-to-noise ratio of the measurement.

Generally, a collector mirror as applied in an EUV radiation source is equipped with a grating of IR radiation configured to reduce reflection towards a second focus of the collector mirror, such as the intermediate focus IF shown in FIG. 2. Such a grating is shown schematically in FIG. 10. FIG. 10 schematically shows a portion 1400 of a collector mirror, including a grating 1410 having a periodic P. FIG. 10 further shows a test radiation beam 1420 configured to irradiate a restricted portion of the collector mirror portion 1400. The radiation beam 1420 has a cross section Pb corresponding to the size of the light spot or restricted portion of the irradiated collector mirror.
The inventors have thought that the edge 1410.1 of the grating may cause measurement disturbances as performed. In order to avoid such disturbances, it has been found that it may be advantageous to choose the size of the light spot irradiated by the radiation beam 1420 as an integer multiple of the periodicity of the grating, that is, select Pb = n × P, where n is an integer.

FIG. 11 schematically shows a cross-sectional view of a system according to the present invention, as drawn on a whiteboard 1500 by the inventor HF.

In the embodiment of the system according to the invention as described above, the system according to the invention is described as being used for the detection or detection of collector lenses, in particular collector lenses having a first focus and a second focus. Test the system. When the mirror to be tested has a first focus and a second focus, as described above, it is advantageous to configure a test radiation subsystem in one of the first focus and the second focus and to place the test radiation subsystem in the first focus and the second focus. The sensor subsystem is configured in the other of the focal points. Thereby, the properties of a mirror that the radiation emitted from the first focus will reach the second focus (or vice versa) can be used, regardless of the angle at which the radiation is emitted. However, the present invention can also be implemented to detect or test other mirrors, that is, mirrors that do not have a first focus and / or a second focus.

In the absence of a first focus and / or a second focus, appropriate measures may need to be taken to ensure that the test radiation, as emitted by the test radiation subsystem and reflected by the mirror, is transmitted by the sensor sub-system of the system according to the invention System capture. Such measures may include, for example, the application of one or more actuators or motors that enable the sensor subsystem and / or the test radiation subsystem and / or the radiation limiter subsystem and / or being tested Or detect the mirror displacement.

A system according to the invention including such measures is schematically illustrated in FIG. 12.

FIG. 12 schematically illustrates a system 1100 according to the present invention, which is configured to detect a mirror 1110 having a reflective surface 1110.1. The reflective surface 1110.1 may generally have any shape. The mirror 1110 may be, for example, a substantially flat mirror, a parabolic mirror, or a free-form mirror. The system according to an embodiment of the present invention includes a test radiation subsystem 1120, a sensor subsystem 1130, and a radiation limiter subsystem. The radiation limiter subsystem includes a first radiation limiter subsystem 1140.1 and a second radiation limiter subsystem. System 1140.2. These subsystems have essentially the same functionality as the subsystems described above. In the embodiment as shown, the system further includes an actuator subsystem 1150 configured to displace the sensor subsystem 1130 and the radiation limiter subsystem 1140.2. In detail, the actuator subsystem 1150 is configured to displace the sensor subsystem 1130 and the radiation limiter subsystem 1140.2 along the X axis.

The system 1100 according to the present invention includes a test radiation subsystem 1120 operable to project test radiation 1120.1 onto a mirror 1100. Regarding the type of test radiation, especially the wavelength or wavelength range of the radiation, similar considerations apply as described above. In an embodiment, the test radiation subsystem 1120 is configured to generate test radiation across an angle α ₀ so that the entire mirror 1100 can be irradiated in principle. Note that the diagram of FIG. 12 represents the collector mirror 300 in a two-dimensional cross section, and in practice, test radiation is typically emitted in three dimensions. In an embodiment, the test radiation subsystem 1120 is configured to generate test radiation that spans an angle less than the angle α ₀ . In such embodiments, the entire mirror 1100 can still be scanned or irradiated, for example, by rotating the test radiation subsystem 1120 or a portion thereof.

The system 1100 according to the present invention further includes a sensor subsystem 1130, which is operable to receive test radiation reflected from the mirror 1100 toward the sensor subsystem 1130, such as test radiation indicated by arrow 1142. In one embodiment, as described above, for example, the sensor subsystem 1130 may include one or more sensors or detectors for measuring test radiation reflected from the mirror 1110.

According to the present invention, the system 1100 for testing the mirror 1110 further includes a radiation limiter subsystem, and the radiation limiter subsystem includes a first radiation limiter subsystem 1140.1 and a second radiation limiter subsystem 1140.2. The radiation limiter subsystems 1140.1, 1140.2 are configured to limit the test radiation as received by the sensor subsystem 1130 to the test radiation reflected from the restricted portion of the mirror 1110. Thus, the radiation measured or detected by the sensor subsystem 1130 will only involve radiation reflected from the restricted portion of the mirror 300. In the embodiment as shown, the restricted portion of the mirror is indicated by the mirror segment 1110.2. By limiting the radiation as received by the sensor subsystem 1130 to the radiation reflected from the restricted portion 1110.2 of the mirror, we can evaluate the effectiveness of that particular part of the mirror, such as evaluating the reflectance of that part.

In the embodiment as shown, the radiation limiter subsystem 1140.1 is configured to pass only a small portion 1141 of the generated radiation 1120.1 toward the mirror 1110. A small portion 1141 of the radiation 1120.1 opposes an angle much smaller than the angle α ₀ . To achieve that, the radiation limiter subsystem 1140.1 includes a shielding member with an aperture, such as a tubular aperture through which a small portion of the test radiation 1120.1 can pass. The radiation limiter subsystem 1140.1 thus enables only a restricted portion, such as the portion 1110.2 of the mirror, to be irradiated by the test radiation generated by the test radiation subsystem 330. In a similar manner, the radiation limiter subsystem 1140.2 is configured to allow only the sensor subsystem to receive test radiation from the restricted portion of the mirror 1110. It should be noted that the first radiation limiter subsystem 1140.1 and the second radiation limiter subsystem 1140.2 may therefore have substantially the same functionality and structure as the radiation limiter subsystem as described in FIGS. 3 and 6. It should be noted that in a similar manner as described in FIG. 3, any of the first radiation limiter subsystem 1140.1 and the second radiation limiter subsystem 1140.2 may be omitted.

According to the present invention, the system further includes a control subsystem 1170 configured to be controlled, for example, by providing control signals 1170.1 and 1170.2 to the first radiation limiter subsystem 1140.1 and the second radiation limiter subsystem 1140.2. Movement of these radiation limiter subsystems. In detail, the control subsystem 1170 is configured to control the position of the radiation limiter subsystem such that the restricted portion of the mask irradiated by the test radiation can be changed. Thus, the control subsystem 1170 may, for example, be configured to control the movement of the radiation limiter subsystem along a series of different positions, thereby limiting the test radiation, as received by the sensor subsystem 1130, to that of the mirror 1110. A series of test radiation reflected by different restricted sections. In this way, the effectiveness of different restricted parts of the mirror 1110 can be evaluated, such as the reflectance of these parts.

In one embodiment of the present invention, a set of different restricted portions substantially covers the entire mirror 1110.

In one embodiment of the present invention, the radiation limiter subsystem may include one or more actuators to change the orientation of the test radiation 1141 projected onto the mirror 1110, and to change the orientation as measured by the sensor subsystem 1130. Direction of received test radiation 1142.

In one embodiment, the control subsystem 1170 may be configured to direct the beam or beam-shaping test radiation to a plurality of different restricted portions of the mirror 1110, one restricted portion being connected to another restricted portion for guidance. . Such sequential projection of the test radiation beam onto different restricted portions of the mirror 1110 may also be referred to as scanning the mirror using the test radiation beam. During such a scanning procedure by which a portion of the mirror 1110 or the entire mirror is scanned, the sensor subsystem 1130 may generate a set of measurement data representative of test radiation reflected from different restricted portions of the collector mirror 1110. Such measurement data may be provided to the control subsystem 1170 of the system according to the invention, for example via a data channel, as indicated by arrow 1170.3. In one embodiment, the received measurement data 1170.3 may be processed by the processing unit 1180 of the control subsystem 1170, for example. Such a processing unit may be embodied, for example, as a processor, a microprocessor, a computer, or the like. Such processing unit 1180 may include, for example, a memory unit for storing measurement data.

In an embodiment, the processing unit 1180 may be configured to process the measurement data in order to determine a spatial reflectance distribution of at least a portion of the collector mirror. In such embodiments, the measurement data representing the test radiation reflected from different restricted portions of the mirror 1110 and the data representing the generated or emitted test radiation may be compared to determine the reflection of the different restricted portions of the mirror. rate. An example of a measure of reflectance is the ratio of the amount of test radiation received to the amount of test radiation generated or emitted, and the amount of test radiation generated or emitted on the one hand and the amount of test radiation received on the other The difference. Therefore, in one embodiment of the present invention, the measurement data obtained from the sensor subsystem 1130 can be supplemented with active measurement data, and the source measurement data represents the amount of test radiation emitted or generated during the scanning procedure. Such source measurement data may be provided to the processing unit 1180 of the control subsystem 1170 via a data channel, for example.

An embodiment of a system according to the present invention as shown schematically in FIG. 12 further includes an actuator subsystem 1150 configured to displace the sensor subsystem 1130 and the radiation limiter subsystem 1140.2. The goal of this actuator subsystem 1150 is to ensure that test radiation reflected from the mirror is captured by the sensor subsystem 1130, such as the radiation indicated by element symbol 1142. In the absence of the first focus and the second focus, those skilled in the art should know that the test radiation passing through different parts of the guide mirror will also be reflected to different parts. Therefore, in one embodiment of the present invention, the fact that the test radiation at different locations on the guide mirror will be reflected to different locations is provided by providing displacements of the sensor subsystem 1130 and the radiation limiter subsystem 1140.2.

Such a required displacement is schematically depicted in FIG. 12. In detail, in FIG. 12, the dashed arrow 1143 indicates the test radiation passing through the restricted portion 1110.3 of the guide mirror 1110, and the restricted portion 1110.3 is located at a different position on the mask than the restricted portion 1110.2. The dashed arrow 1144 indicates the test radiation reflected from the restricted portion 1110.3. It can be seen that compared to the reflected test radiation 1142, the reflected test radiation 1144 is directed at different locations and at different angles. In order to capture the reflected test radiation 1144, the sensor subsystem 1130 and the radiation limiter subsystem 1140.2 may be displaced to a location indicated schematically by a dashed line 1190. The dashed line 1190 therefore schematically illustrates the location of the sensor subsystem 1130 and the orientation of the radiation limiter subsystem 1140.2 that enables the capture of test radiation 1144. In one embodiment of the present invention, the control unit 1170 may be configured to target the test radiation based on the known shape or predetermined shape information of the mirror to be detected and the known relative positions of the test radiation subsystem and the mirror. A specific restricted portion of the mirror determines where the reflected test radiation will be directed. Based on this determined direction, the control unit 1170 may then be configured to control the actuator subsystem 1150 such that the sensor subsystem 1130 and the radiation limiter, for example, by providing the actuator subsystem 1150 with an appropriate control signal 1170.4. Subsystem 1140.2 is moved to a suitable location to capture the reflected radiation.

In an embodiment, the actuator subsystem 1150 may, for example, include one or more actuators for displacing the sensor subsystem 1130 and the radiation limiter subsystem 1140.2, such as an electromagnetic actuator or a piezoelectric actuator. Actuators and / or one or more linear or planar motors. In an embodiment, the actuator subsystem 1150 may be configured to displace the sensor subsystem 1130 and the radiation limiter subsystem 1140.2 in multiple degrees of freedom. In the embodiment as shown, the actuator subsystem 1150 may, for example, be configured to displace the sensor subsystem 1130 and the radiation limiter subsystem 1140.2 in the X and Y directions, the Y direction being perpendicular to the The indicated XZ plane.

In the embodiment as shown, the test radiation subsystem 1120 is mounted to the frame 1200, and the sensor subsystem 1130 and the radiation limiter subsystem 1140.2 can be displaced relative to the frame 1200 by the actuator subsystem 1150. In such embodiments, the relative positions of the test radiation subsystem and the mirror to be detected may remain fixed during the inspection.

As an alternative to displacing the sensor subsystem 1130 and the radiation limiter subsystem 1140.2 by the actuator subsystem 1150, the system according to the present invention may also include a mirror 1110 configured relative to the test radiation subsystem 1120 Displacement actuator subsystem.

Such an embodiment is schematically depicted in FIG. 13. Except for the following cases, the system 1300 as shown schematically in FIG. 13 substantially corresponds to the system 1100 shown in FIG. 12. In the embodiment as shown in FIG. 13, the test radiation subsystem 1120 and the sensor subsystem 1130 are mounted to the common frame 1200 together with the radiation limiter subsystem. In the embodiment as shown, the test radiation subsystem 1120 and the sensor subsystem 1130 are therefore considered to have a fixed relative position. To ensure that the test radiation reflected from the mirror 1110 is reflected toward the sensor subsystem 1130, the system is provided with an actuator subsystem 1155 configured to displace the mirror 1110. In detail, the actuator subsystem 1155 is configured to displace the mirror so that the reflected radiation 1145 reflected from the restricted portion 1110.3 is directed to the same location as the reflected radiation 1142. In detail, in the embodiment as shown, the actuator subsystem 1155 is configured to tilt or rotate the mirror 1110 such that the test radiation 1143 is reflected as a portion of the radiation 1145 toward the sensor subsystem 1130. It should be noted that in order for the sensor subsystem 1130 to capture the reflected radiation 1145, the radiation limiter subsystem 1140.2 may need to be rotated. In a similar manner as described with reference to FIG. 12, the control unit 1170 may be configured to test radiation based on the known shape or predetermined shape information of the mirror to be detected and the known relative positions of the test radiation subsystem and the mirror. A specific restricted portion of the aiming mirror determines where the reflected test radiation will be directed. Based on this determined direction, the control unit 1170 may then be configured to control the actuator subsystem 1155 to move the mirror to an appropriate location or position, for example, by providing the actuator subsystem 1155 with an appropriate control signal. The test radiation received by the mirror is reflected to the sensor subsystem.

Alternatives for displacement of the sensor subsystem 1130 and the radiation limiter subsystem 1140.2 by the actuator subsystem 1150 or displacement of the mirror 1110 with respect to the test radiation subsystem by the actuator subsystem 1155 should be used to make the test The actuator subsystem that the radiation subsystem 1120 is displaced relative to the mirror 1110 thereby arranges for the reflected radiation to reach the sensor subsystem 1130 regardless of which part of the mirror is irradiated.

In the embodiment as described with reference to FIGS. 12 and 13, the actuator subsystem is used to ensure that an optical path for test radiation is established between the test radiation subsystem and the sensor subsystem. In such embodiments, the actuator subsystem is therefore used to ensure that the test radiation subsystem, mirror, and sensor subsystem are in an appropriate relative position and orientation so that a particular portion of the mirror being tested or tested is illuminated and The test radiation reflected by the mirror is captured by the sensor subsystem. According to the invention, the optical path of the test radiation will also pass through the radiation limiter subsystem or several radiation limiter subsystems. As described above, these systems can also be positioned or displaced by the actuator subsystem.

In one embodiment of the invention, an actuator subsystem is further applied to control the angle at which the test radiation is incident on the mirror. It can be seen in FIG. 12 that the incident angle of the test radiation 1141 is different from the incident angle of the test radiation 1143. This may be bad. In detail, it may be necessary to test the mirror, for example, to determine the reflectance of the mirror so that the test radiation is applied in substantially the same way--that is, at the same angle of incidence--as in Occurs during normal use of the mask. For a particular application, the radiation beam may illuminate the mirror across the entire mirror surface at substantially the same angle. To test such a mirror, it may therefore be advantageous to ensure that the test radiation illuminates the mirror at an appropriate angle regardless of which part of the mirror is irradiated. Such a configuration can be ensured, for example, by controlling the relative position and / or orientation of the test radiation subsystem and the mirror. Such control may be established, for example, by applying an actuator subsystem configured to control the relative position and / or orientation of the test radiation subsystem and the mirror. Such actuator subsystems can be controlled, for example, by a control subsystem as described above, whereby the control subsystem is configured to generate actuators for controlling the actuators based on the required angle of incidence information of the tested or inspected mirror. Control signals of the system.

Thus, in one embodiment of the invention, the actuator subsystem or several actuator subsystems as applied may serve a dual purpose:
-Provide an optical path for testing radiation between the test radiation subsystem and the sensor subsystem, and
-Make sure that the test radiation is shining on a mirror that is tested at an appropriate or desired angle of incidence.
To meet both requirements, movement or displacement in additional or multiple degrees of freedom may be required.
In one embodiment of the present invention, the actuator sub-assembly may, for example, include a 5 or 6 degree of freedom robot arm to displace the test radiation subsystem and / or the sensor subsystem.

It can be pointed out that the above-mentioned embodiments of the system according to the invention can also be combined. In such a combined embodiment, we can, for example, apply an actuator subsystem that is configured to displace both the mirror and the test radiation subsystem, or to displace both the mirror and the sensor subsystem. Or displacement, or any other combination.

In such embodiments, it may be advantageous, for example, to distribute the required degrees of freedom needed to actuate across different components.

Referring to the embodiment of FIG. 12, it may be advantageous, for example, to configure the actuator subsystem to scan the mirror 1110, the actuator subsystem being configured to displace the sensor subsystem along the X-axis and the mirror Displace along the Y axis. Thus, by using two linear motors or actuators, a two-dimensional scan of the surface of the mirror can be obtained.

As mentioned, the system as described above with reference to FIGS. 12 and 13 enables detection or testing of mirrors that do not have a first and a second focus. These systems can therefore be applied to evaluate the reflectivity of mirrors of any shape or mirrors with a single focus.

In general, it will be apparent from the examples given above that we will need to apply the actuator subsystem and then enable displacement or rotation in at least two degrees of freedom (applied to the same component of the system or different components) in order to scan Or inspect the surface of the mirror. However, in the case of a mirror having an optical axis--that is, an axis along which rotational symmetry exists--it may be sufficient to make any component of the system--that is, a mirror or test radiator The system or sensor subsystem--displaces in only one degree of freedom--for example, translational degrees of freedom along the optical axis. To achieve this, both the test radiation subsystem and the sensor subsystem should be configured on the optical axis, as shown, for example, in FIGS. 3 and 6. In such configurations, we can, for example, use a system as shown in Figures 3 and / or 6 to test a parabolic mirror, with a new configuration configured to translate the sensor subsystem along the optical axis to ensure that the Reflected Actuator Subsystem.

Although specific embodiments of the invention have been described above, it should be understood that the invention may be practiced in other ways than described. The behavior of the system can be largely driven by a computer program containing one or more sequences of machine-readable instructions for implementing certain steps of the method as disclosed above or by a data storage medium storing such computer programs (Such as semiconductor memory, magnetic disks, or optical disks). The above description is intended to be illustrative, and not restrictive. Therefore, it will be apparent to those skilled in the art that modifications can be made to the invention as described without departing from the scope of the patent application scope set forth below.

20‧‧‧ Extreme ultraviolet (EUV) radiation beam

21‧‧‧ Beam

22‧‧‧faceted scene mirror device

24‧‧‧ Faceted pupil mirror device

26‧‧‧patterned beam

28‧‧‧Reflective element

30‧‧‧Reflective element

100‧‧‧lithography system

210‧‧‧ Extreme ultraviolet (EUV) radiation emitting plasma

220‧‧‧Containment structure

221‧‧‧ Aperture

223‧‧‧laser

224‧‧‧laser energy

226‧‧‧ fuel source

228‧‧‧ Fuel Stream

230‧‧‧ Retainer

240‧‧‧beam delivery system

242‧‧‧source control module

260‧‧‧ sub-beam

262‧‧‧Adjustment and Masking Module

266‧‧‧Synchronous mobile

268‧‧‧Synchronous mobile

300‧‧‧ Collector mirror

300.1‧‧‧mask clip

310‧‧‧ First Focus

320‧‧‧Second Focus

330‧‧‧Test Radiation Subsystem

330.1‧‧‧Test radiation

340‧‧‧Sensor Subsystem

342‧‧‧test radiation

360‧‧‧First Radiation Limiter Subsystem

360.1‧‧‧shielding parts

360.2‧‧‧ Tubular Aperture

370‧‧‧control subsystem

370.1‧‧‧Control signal

370.2‧‧‧Measurement data obtained

370.3‧‧‧Source measurement data

380‧‧‧processing unit

390‧‧‧Second Radiation Limiter Subsystem

390.1‧‧‧shielding parts

390.2‧‧‧Aperture tube

410‧‧‧ Aperture

420‧‧‧ radiation source

420.1‧‧‧ part of the radiation

420.2‧‧‧Reflected radiation

420.3‧‧‧ radiation beam

420.4‧‧‧ Collimated beam

430‧‧‧First mirror

440‧‧‧Second Mask

450‧‧‧ Aperture

460‧‧‧Aperture tube

470‧‧‧parts

520‧‧‧ radiation source

520.1‧‧‧ part of the radiation

520.2‧‧‧Reflected radiation

520.3‧‧‧ Filtered radiation

530‧‧‧Face Mirror Assembly

540‧‧‧Face Mirror Assembly

550‧‧‧Focus

620‧‧‧ radiation source

620.1‧‧‧ part of radiation

620.2‧‧‧Reflected radiation

620.3‧‧‧ Collimated beam / test radiation beam

620.4‧‧‧ radiation

630‧‧‧First mirror

640‧‧‧first mirror

650‧‧‧source sensor

660‧‧‧ Aperture

700‧‧‧ sensor subsystem

700.1‧‧‧Sensor

700.2‧‧‧active area

700.3‧‧‧ output

700.4‧‧‧Measurement signal

710.1‧‧‧beam

710.2‧‧‧beam

750‧‧‧ sensor subsystem

750.1‧‧‧Sensor

750.2‧‧‧Sensor

750.3‧‧‧Sensor

760‧‧‧Sensor Subsystem

760.1‧‧‧Sensor

760.2‧‧‧active area

770‧‧‧Actuator / actuator configuration

780‧‧‧ axis

790‧‧‧Sensor Subsystem

790.1‧‧‧ Sensor

795‧‧‧Aperture tube

800‧‧‧ Sensor Subsystem

800.1‧‧‧Sensor

810‧‧‧Face Mirror

820‧‧‧face mirror

830.1‧‧‧Test radiation

830.2‧‧‧Reflected radiation

840‧‧‧Aperture tube

850‧‧‧ First Focus

900‧‧‧ Sensor Subsystem

900.1‧‧‧ Sensor

910‧‧‧Face Mirror

920‧‧‧Face Mirror

930.1‧‧‧Test radiation

930.2‧‧‧Reflected radiation

940‧‧‧Aperture tube

950‧‧‧ Hemisphere shield

960‧‧‧Aperture tube

970‧‧‧Actuator configuration

970.1‧‧‧First actuator

970.2‧‧‧Second actuator

975‧‧‧ Center

1000‧‧‧test radiation beam

1100‧‧‧ Collector Mirror / System

1110‧‧‧face mirror

1110.1‧‧‧ reflective surface

1110.2‧‧‧ Mask clips / restricted parts

1110.3‧‧‧ Restricted

1120‧‧‧test radiation subsystem

1120.1‧‧‧Test radiation

1130‧‧‧Sensor Subsystem

1140.1‧‧‧ Radiation Limiter Subsystem

1140.2‧‧‧ Radiation Limiter Subsystem

1141‧‧‧Small part

1142‧‧‧Test radiation / reflected radiation

1143‧‧‧Test radiation

1144‧‧‧Test radiation

1145‧‧‧Reflected radiation

1150‧‧‧Actuator Subsystem

1155‧‧‧Actuator Subsystem

1170‧‧‧control unit

1170.1‧‧‧ Radiation Limiter Subsystem

1170.2‧‧‧ Radiation Limiter Subsystem

1170.3‧‧‧Measurement data

1170.4‧‧‧Control signal

1180‧‧‧processing unit

1190‧‧‧parts

1200‧‧‧Frame

1210‧‧‧First vacuum chamber / container

1220‧‧‧Frame

1230‧‧‧ Outer frame

1240‧‧‧Test Radiation Subsystem

1240.1‧‧‧Test radiation

1250‧‧‧Second Focus

1255‧‧‧ First Focus

1260‧‧‧Sensor Subsystem

1260.1‧‧‧Test radiation

1270‧‧‧First Radiation Limiter Subsystem

1270.1‧‧‧shielding parts

1270.2‧‧‧Aperture tube

1280‧‧‧Second Radiation Limiter Subsystem

1285‧‧‧Possible displacement

1290‧‧‧Second vacuum chamber / container

1300‧‧‧wall

1300.1‧‧‧wall section

1300.2‧‧‧wall section

1310‧‧‧Gap

1320‧‧‧purified gas subsystem

1400‧‧‧ Collector mirror section

1410‧‧‧Grating

1410.1‧‧‧Edge

1420‧‧‧Test radiation beam

1500‧‧‧ Whiteboard

B‧‧‧ radiation beam

C ‧‧‧ Target section

CO‧‧‧Near normal incidence collector mirror

HF‧‧‧ Inventor

IF‧‧‧Virtual Source / Intermediate Focus

IL‧‧‧Lighting System

M1‧‧‧ Mask alignment mark

M2‧‧‧ Mask alignment mark

MA‧‧‧ Patterned Device

MT‧‧‧ support structure

MO‧‧‧Master Laser / Seed Laser

O‧‧‧ Optical axis

P‧‧‧ Periodic

P1‧‧‧Substrate alignment mark

P2‧‧‧ substrate alignment mark

Pb‧‧‧ cross section

PM‧‧‧First Positioner

PS‧‧‧ projection system

PS1‧‧‧Position Sensor

PS2‧‧‧Position Sensor

PW‧‧‧Second Positioner

SO‧‧‧Source Collector Module

W‧‧‧ substrate

WT‧‧‧ Substrate

X‧‧‧ axis / direction

Y‧‧‧ axis / direction

Z‧‧‧ axis / direction

α‧‧‧ angle

α ₀ ‧‧‧ angle

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings, in which corresponding component symbols indicate corresponding parts, and in the drawings:

FIG. 1 schematically depicts a lithography system according to an embodiment of the present invention;

Figure 2 is a more detailed view of the system of Figure 1 and shows a novel monitoring and control system for EUV radiation sources;

Figure 3 schematically shows a cross section of one embodiment of a system according to the invention;

4a to 4c schematically show cross-sectional views of a test radiation subsystem as may be applied in the present invention;

5a to 5f schematically show cross-sectional views of a sensor subsystem as may be applied in the present invention;

Fig. 6 schematically shows a cross section of another embodiment of a system according to the invention;

Fig. 7 schematically shows a radiation limiter subsystem as may be applied in a system according to the invention;

Figure 8 shows schematically a cross section of a system according to the invention in a calibration position;

Fig. 9 schematically shows a cross section of a further embodiment of a system according to the invention;

Fig. 10 schematically shows a part of a collector mirror as can be detected by a system according to the invention.

Fig. 11 schematically shows a system according to the invention on a whiteboard and the inventor.

FIG. 12 schematically shows a cross section of one embodiment of a system according to the invention for testing or detecting a mirror;

Fig. 13 schematically shows a cross section of another embodiment of a system according to the invention for testing or detecting a mirror.

Claims (26)

A system configured to test a collector mirror having a first focus and a second focus, the system comprising: A test radiation subsystem operable to project test radiation from the second focus onto the collector mirror; A sensor subsystem operable to receive test radiation reflected from the collector mirror toward the first focus; and A radiation limiter subsystem operable to limit the test radiation as received by the sensor subsystem to test radiation reflected from a restricted portion of the collector mirror; A control subsystem operable to control the radiation limiter subsystem to move along one of a series of different positions, thereby limiting the test radiation as received by the sensor subsystem to the collector mirror A series of test radiation reflected by different restricted sections. The system of claim 1, wherein the control subsystem includes a processing unit configured to perform one of the following operations: Receiving measurement data from the sensor subsystem, the measurement data representing test radiation reflected from different restricted portions of the series of the collector mirror; The measurement data is processed to determine a spatial reflectance distribution of at least a portion of the collector mirror. The system of claim 1 or 2, wherein the test radiation comprises EUV radiation. The system of claim 3, wherein the test radiation subsystem includes an EUV source for generating the EUV radiation. The system of claim 3, wherein the test radiation subsystem includes a multi-layered mirror assembly for filtering the EUV radiation. The system of claim 5, wherein the multi-layered mirror assembly includes a pair of multi-layered mirrors for performing a spectrum of one of the EUV radiation projected by the test radiation subsystem from the second focus Shape. The system of claim 6, wherein the pair of multi-layer mirrors is configured as a Schwarzschild objective lens. If the system of claim 1 or 2, wherein the sensor subsystem includes a sensor, the sensor is operable to receive the test radiation reflected from the collector mirror towards the first focus and generate a representation such as A measurement signal received as one of the test radiation. The system of claim 8, wherein the sensor subsystem includes a multi-layer mirror assembly for filtering the test radiation as received by the sensor. The system of claim 8, wherein the sensor comprises an EUV photodiode. The system of claim 1 or 2, wherein the test radiation subsystem includes a source sensor configured to generate a source measurement signal representative of the test radiation projected by the test radiation subsystem . The system of claim 1 or 2, wherein the radiation limiter subsystem includes a shielding component having an aperture in the shielding component, and the shielding component is disposed in an optical path of the test radiation. The system of claim 12, wherein the aperture is formed by an aperture tube of the radiation limiter subsystem. The system of claim 12, wherein the radiation limiter subsystem is configured in an optical path of the test radiation between the second focus and the collector mirror. The system of claim 12, wherein the radiation limiter subsystem is configured in an optical path of the test radiation between the second focus and the collector mirror. The system of claim 12, wherein the radiation limiter subsystem includes: A first shielding member having a first aperture in the first shielding member, the first shielding member being disposed in an optical path of the test radiation between the second focus and the collector mirror; A second shielding member has a second aperture in the second shielding member, and the second shielding member is disposed in an optical path of the test radiation between the collector mirror and the first focus. The system of claim 16, wherein the control subsystem is configured to control movement of one of the first shielding member and the second shielding member so as to be at the second focus via both the first aperture and the second aperture An optical path is established with the first focus for the test radiation. The system of claim 16 wherein the control subsystem is configured to perform one of the system's calibrations by: Positioning both the first aperture and the second aperture along an optical axis passing through the first focus and the second focus; Controlling the test radiation subsystem to emit test radiation directly toward the sensor subsystem through both the first aperture and the second aperture; Receiving a measurement signal representing one of the sensor subsystems as the test radiation is received; Receiving a source measurement signal of the test radiation subsystem representing the test radiation projected by the test radiation subsystem; and The system is calibrated based on the measurement signal and the source measurement signal. The system of claim 1 or 2, wherein the test radiation subsystem comprises a Xe, Li or Sn radiation source. A system configured for testing a mirror, the system comprising: A test radiation subsystem operable to project test radiation onto the mirror; A sensor subsystem operable to receive test radiation reflected from the mirror; and A radiation limiter subsystem operable to limit the test radiation as received by the sensor to test radiation reflected from a restricted portion of the mirror; A control subsystem operable to control the radiation limiter subsystem to move along one of a series of different positions, thereby limiting the test radiation as received by the sensor to a series from the mirror Test radiation reflected by different restricted sections. The system of claim 20, further comprising: An actuator subsystem configured to displace at least one of the test radiation subsystem, the sensor subsystem, the radiation limiter subsystem, and the mirror. The system of claim 21, wherein the control subsystem is configured to control the actuator subsystem to establish an optical path for the test radiation between the test radiation subsystem and the sensor subsystem. A method for testing a collector mirror having a first focus and a second focus, the method comprising: projecting test radiation from the second focus onto the collector mirror; and receiving by a sensor from the collector The mirror reflects test radiation towards the first focus; and limits the test radiation as received by the sensor to test radiation reflected from a restricted portion of the collector mirror; controls a radiation limiting subsystem along One of a series of different positions is moved, thereby limiting the test radiation as received by the sensor to test radiation reflected from each of a series of different restricted portions of the collector mirror. The method of claim 23, wherein the step of limiting the test radiation comprises: Arranging a first shielding member in an optical path of the test radiation between the second focus and the collector mirror, and having a first aperture in the first shielding member; and A second shielding member is disposed in an optical path of the test radiation between the collector mirror and the first focus, and the second shielding member has a second aperture. The method of claim 24, wherein the step of controlling a movement includes: Controlling one of the first shielding member and the second shielding member to move so as to establish an optical for the test radiation between the second focus and the first focus via both the first aperture and the second aperture path. The method of claim 25, further comprising a calibration step of the test method, the calibration step comprising: positioning the first aperture and the second aperture along an optical axis passing through the first focus and the second focus Control of the test radiation to be emitted directly toward the first focus through both the first aperture and the second aperture; receive a measurement signal representing one of the test radiations as received; receive a measurement signal representing the emitted test radiations A source measurement signal; and calibrating the test method based on the measurement signal and the source measurement signal.