Testing system for a camera and methods for testing a camera

Abstract

A test system for a camera, comprising a camera (23) and a first collection plate (101). The camera (23) comprises a camera housing (25) and a vacuum flange (31) formed on the camera housing (25). The vacuum flange (31) is configured so that the camera (23) can be attached to a vacuum chamber (41). The camera housing (25) carries an image sensor (24). The image sensor (24) comprises an image sensor surface layer (28). The first collection plate (101) comprises a first collection plate surface layer (102). The first collection plate surface layer (102) corresponds to the image sensor surface layer (28). The invention also relates to a method for testing a camera, in particular an EUV camera.

Description

[0001] The invention relates to a testing system for a camera and a method for testing a camera. The camera can, in particular, be an EUV camera.

[0002] Photomasks are used in microlithographic projection exposure systems for the fabrication of integrated circuits with extremely small structures. The photomask is illuminated with very short-wavelength, extreme ultraviolet (EUV) radiation and imaged onto a lithography object to transfer the mask structure to the object.

[0003] For a high-quality image produced on the lithographic object, it is essential that the photomask is dimensionally accurate and free from impurities. It is known that photomasks are inspected before use in a microlithographic projection exposure system or during downtime. For this purpose, an aerial photograph of the photomask or a section of it is taken, with the photomask projected not onto a lithographic object, but onto an EUV image sensor of a camera. Based on the image on the EUV image sensor, it can be assessed whether the photomask is free of defects and impurities.

[0004] The inspection is typically performed in a photomask inspection system with a vacuum housing, where a vacuum is applied to the housing during the inspection. Camera components, such as the image sensor, are exposed to the vacuum during the inspection.

[0005] The image sensor includes an image sensor surface layer. The image sensor surface layer is a protective layer designed to shield the image sensor from the harmful effects of EUV light.

[0006] During the inspection process, the EUV light affects the camera's surface, particularly the image sensor surface layer. This can cause particles to be released from the image sensor surface layer, leading to contamination (e.g., with carbon) of the image sensor itself, as well as other parts of the photomask inspection system, such as the projection mirror.

[0007] To counteract this, the inspection system, including the camera, is purged with a purge gas such as hydrogen or helium. Although purging helps remove EUV-induced contaminants, the purge gas also erodes surface layers of components within the inspection system, such as the image sensor surface layer. Outgassing effects can occur in the camera, and especially in the image sensor, caused by the vacuum and the purge gas.

[0008] It is therefore foreseeable that the camera, and in particular the image sensor, will be affected over time by the influence of EUV light and purge gas. As a result, the image sensor will gradually lose its image quality and will need to be replaced after a certain period to maintain the inspection system's performance.

[0009] The use of cameras in EUV inspection systems for photomasks is a relatively recent development. Therefore, there is currently no data on the long-term performance of cameras used in these systems. However, it is desirable to be able to estimate the lifespan of cameras in such systems, for example, to estimate long-term operating costs.

[0010] A micro-format measuring device for treating a semiconductor wafer is known from CN 1 400 450 A. DE 20 2010 015 912 U1 discloses an electrical feedthrough arrangement suitable for ultra-high vacuum applications for a camera chip. DE 10 2008 000 551 A1 discloses a method for cleaning an EUV lithography device and a method for measuring the residual gas atmosphere in an EUV lithography device.

[0011] It is therefore an object of the invention to provide a testing system for a camera and a method for testing a camera, with which the service life of cameras in inspection systems for photomasks can be estimated. This purpose is achieved by the features of the independent claims. Advantageous embodiments are specified in the dependent claims.

[0012] According to the invention, the test system for a camera comprises a camera and a first collection plate. The camera has a camera housing and a vacuum flange formed on the camera housing. The vacuum flange is configured to attach the camera to a vacuum chamber. The camera housing carries an image sensor. The image sensor comprises an image sensor surface layer, and the first collection plate comprises a first collection plate surface layer, the first collection plate being designed to collect EUV-induced contaminants such as particles and emissions caused by exposure of the image sensor to EUV light in the test system. The first collection plate surface layer corresponds to the image sensor surface layer, such that the composition of the image sensor surface layer is identical to the composition of the first collection plate surface layer.

[0013] The invention is based on the fact that higher EUV intensities can be used for a shorter period during an exposure phase in the test system to predict the long-term behavior of the camera under test, which is exposed to lower EUV intensities for a longer period during operation in a photomask inspection system. In an evaluation phase, surfaces of parts of the test system, e.g., the first surface layer of the collection plate, can be analyzed.

[0014] The first collection plate can capture EUV-induced contaminants such as particles and emissions caused by the exposure of the image sensor to EUV light in the test system. Since the surface layer of the first collection plate corresponds to the surface layer of the image sensor, evaluation of the image sensor surface layer is possible independently of the image sensor itself. In other words, the first collection plate has the advantage that the image sensor surface layer is present again separately from the image sensor in the test system (namely, in the form of the first collection plate surface layer) and is exposed to the same test conditions during the exposure phase (e.g., EUV light intensity and purge gas environment).With the camera and the first collection plate, the testing system according to the invention thus enables a combination of both: the evaluation of the imaging performance of the image sensor and the independent surface analysis of the image sensor surface layer by analyzing the surface layer of the first collection plate. The combination of both allows conclusions to be drawn about the camera's durability.

[0015] The image sensor surface layer can comprise silicon and boron. In one embodiment, the image sensor surface layer is a layer of back-thinned silicon doped with boron implants. The first collection plate surface layer can comprise silicon and boron. In one embodiment, the first collection plate surface layer is a layer of back-thinned silicon doped with boron implants. The composition of the image sensor surface layer is identical to the composition of the first collection plate surface layer. In a specific embodiment, the entire first collection plate is made of a material that corresponds to the material of the image sensor surface layer.

[0016] The camera can be an EUV camera. The image sensor is then an EUV image sensor, meaning an image sensor sensitive to EUV light. EUV light is light in the extreme ultraviolet spectral range with wavelengths between 5 nm and 100 nm, particularly between 5 nm and 30 nm. Specifically, EUV light can have a wavelength of 13.5 nm. The EUV camera can be configured for use in a photomask inspection system, where the photomask is projected onto the EUV image sensor of the EUV camera.

[0017] The test system can include an evaluation unit for reading and analyzing the electrical signals from the image sensor. The image sensor's performance can be assessed using these electrical signals, both during the evaluation phase and during the exposure phase. For this purpose, the EUV light intensity can be correlated with the electrical signals output by the image sensor, allowing conclusions to be drawn about the condition of the image sensor's surface layer. The evaluation unit can include a memory for storing measurement signals from the image sensor. These measurements can then be read from the memory for later evaluation. The evaluation can include providing a correlation between the image sensor signals and corresponding data from the analysis data of the first surface layer of the image sensor.

[0018] The vacuum flange encloses an illumination area inside or on the camera body. During the exposure phase, this illumination area can be illuminated with EUV light through the vacuum flange. The image sensor and the first image collector plate are located within this illumination area. In other words, both the image sensor and the first image collector plate can be illuminated with EUV light through the vacuum flange during the exposure phase.

[0019] The inspection system may include a second collection plate. The second collection plate comprises a second collection plate surface layer. This second collection plate surface layer corresponds to a material surface layer used in another part of a photomask inspection system. In particular, the second collection plate surface layer may correspond to a mirror surface layer. The mirror surface layer is a material surface layer used in projection mirrors of a photomask inspection system. The second collection plate surface layer may be a ruthenium layer. The second collection plate surface layer may also be a multilayer with alternating layers of molybdenum and silicon.

[0020] The second collection plate can be positioned within the illumination area along with the image sensor and the first collection plate. In other words, the second collection plate can also be exposed to EUV light during the exposure phase via the vacuum flange. Like the first collection plate, the second collection plate can also collect EUV-induced contaminants such as particles and emissions caused by the exposure of the image sensor to EUV light within the inspection system. If the surface layer of the second collection plate corresponds to the mirror surface layer, it is possible to evaluate the long-term behavior of projection mirrors in a photomask inspection system. If the surface layer of the second collection plate corresponds to a material layer used in another part of a photomask inspection system, it is possible to evaluate the long-term behavior of that specific part of the photomask inspection system.The second collection plate thus makes it possible to obtain supplementary information about the long-term behavior of the photomask inspection system, e.g., through surface analysis of the second collection plate's surface layer. In particular, if the second collection plate's surface layer is a ruthenium layer, additional information can be obtained about the long-term behavior of ruthenium-coated optics and mirrors used in the photomask inspection system. The second collection plate can be a substrate coated with a ruthenium layer.

[0021] Preferably, the image sensor and the first collection plate are arranged in a plane perpendicular to the axis of incidence of the EUV light incident on the illumination area. If the test system includes a second collection plate, it is also preferred that the image sensor and the second collection plate are arranged in a plane perpendicular to the axis of incidence of the EUV light incident on the illumination area. Positioning a collection plate in the same plane as the image sensor ensures that the image sensor and the collection plate are exposed to the same test conditions, such as the EUV light intensity.

[0022] A collection plate can be curved or flat.

[0023] The test system can include a vacuum chamber, with the camera attached to the vacuum chamber via a vacuum flange. The vacuum chamber and the camera housing together form a vacuum enclosure. When a vacuum is applied to the vacuum enclosure, the camera housing can be subjected to a pressure differential between its interior and the external environment. The test system can include means for generating a vacuum within the vacuum enclosure. The image sensor and the collection plates can be exposed to the vacuum.

[0024] A structure of the testing system can support the first collection plate and / or the second collection plate. In one embodiment, the camera housing supports the first collection plate and / or the second collection plate. In another embodiment, the vacuum chamber supports the first collection plate and / or the second collection plate.

[0025] During the evaluation phase, it is possible to perform the surface analysis "in situ" while the first and second collection plates are supported by the test system structure. In other embodiments, it may be desirable to remove one collection plate from the test system before performing the surface analysis. For this purpose, one collection plate, i.e., either the first or the second, can be supported by the test system structure via a detachable connection. It is also possible for both the first and second collection plates to be supported by the detachable connection. The detachable connection can include a holder for the collection plate and / or an EUV-resistant adhesive. If a collection plate is detachable, it can be removed from the test system before the surface analysis of the collection plate's surface layer.This is advantageous because the surface layer of the image sensor plate can then be evaluated separately from the camera using surface analysis methods that would otherwise further damage or destroy the image sensor. For example, it is then possible to evaluate the image sensor surface layer spatially separate from the actual image sensor. The surface analysis can be performed using X-ray photoelectron spectroscopy (XPS) or other known surface analysis methods.

[0026] The test system may include an EUV light source. The EUV light source may be located in a vacuum housing and have a line of sight to the illumination area. The line of sight may be straight or deflected, for example, by directing the EUV beam emitted from the EUV light source onto the illumination area via an illumination system consisting of one or more projection mirrors. The illumination system may shape the EUV light into an EUV beam that illuminates the illumination area with uniform intensity. The EUV beam incident on the image sensor may have a diameter of at least 100 mm, preferably at least 300 mm. If the test system includes an EUV light source, it may also include a control unit for controlling the illumination settings of the EUV light source, such as the EUV light intensity or the illumination pattern.

[0027] The testing system can include a first gas inlet for introducing a purge gas into the vacuum housing. The purge gas can be introduced during the exposure phase to create a purge gas environment similar to that found in a photomask inspection system. The camera can then be tested in this purge gas environment. The purge gas can be hydrogen or helium.

[0028] The test system may include a second gas inlet for introducing a dilution gas. After the exposure phase, during which purge gas was introduced into the test system, the dilution gas can be introduced into the vacuum housing during a cleaning phase. The dilution gas can mix with the purge gas to dilute it to a concentration that can be safely discharged. The dilution gas can be nitrogen or another inert gas, such as a noble gas.

[0029] The test system can include a purge gas reservoir that can be connected to the first gas inlet. The test system can also include a dilution gas reservoir that can be connected to the second gas inlet.

[0030] The test system may include a first gas outlet for venting gas from the test system, particularly from the vacuum housing. It is possible to feed the vented gas, especially a mixture of purge gas and dilution gas, to a recovery system so that the purge gas and / or dilution gas can be reused in the test system. For this purpose, the test system may include a recovery reservoir connected to the first gas outlet.

[0031] The test system may include a second gas outlet. This second gas outlet is useful for purging the test system with a gas, such as extremely clean, dry air (XCDA). In this context, purging means the rapid introduction and removal of a gas, particularly during the cleaning phase.

[0032] The testing system can include a modular chamber that forms part of the vacuum housing. The modular chamber can be attached to the vacuum flange of the camera housing. The gas inlets and / or gas outlets can be components of the modular chamber. The modular chamber can then be attached to the camera as a modular adapter to supply the purge gas and / or dilute the purge gas with the dilution gas. When the modular chamber is attached to the camera housing, the camera housing can still be connected to a vacuum chamber via the modular chamber to form a vacuum housing. For this purpose, the modular chamber can include two vacuum flanges: a first vacuum flange for attachment to the camera housing and a second vacuum flange for attachment to a vacuum chamber. This allows the modular chamber to be positioned between the camera housing and the vacuum chamber.The vacuum chamber, the camera housing, and the modular chamber then form the vacuum housing, which is exposed to the vacuum, and the EUV light is directed through the modular chamber onto the illumination area in the camera.

[0033] The test system may include a pressure sensor for monitoring the pressure within the test system, particularly within the vacuum housing.

[0034] The test system can include an adapter plate to provide illumination options. The adapter plate is positioned between the EUV light source and the image sensor to modify the incident EUV beam. The adapter plate can be located inside or attached to the camera housing. It is also possible for the adapter plate to be located inside the modular chamber or the vacuum chamber. The adapter plate can include an aperture, particularly a pinhole. A pinhole allows only a certain portion of the EUV light to reach the image sensor, thus controlling the intensity of the EUV light incident on the illumination area. Pinholes of varying sizes can be provided, which can be used to evaluate the dynamic range of the image sensor. The pinhole can be adjustable in size, or a set of interchangeable pinholes can be provided.It is also possible to provide adapter plates for dark-field and white-field imaging. Dark-field imaging refers to the measurement of the dark current of the image sensor, i.e., the acquisition of so-called dark frames. This is achieved by blocking all incident EUV light from reaching the image sensor. In white-field imaging (sometimes also called "flat-field" imaging), the image sensor is illuminated uniformly and with high intensity, allowing the measurement of the image sensor's dynamic range. Dark-field and white-field images can be used together to perform a so-called "flat-field" correction.

[0035] It is possible that the test system comprises two modular chambers, one for the gas inlets and outlets and a second for the adapter plate. It is also possible that the gas inlets and outlets and the adapter plate are provided together in a single modular chamber.

[0036] The image sensor can consist of a single sensor or multiple sub-sensors. These sub-sensors can be arranged in a matrix or a puzzle configuration. A matrix configuration means that the sub-sensors are arranged side-by-side in rows and columns within a rectangle or square. A puzzle configuration means that adjacent sub-sensors are horizontally or vertically offset from each other, creating steps within the arrangement.

[0037] Particularly when the partial sensors are arranged in a puzzle configuration, not all sections of the image sensor can be fully utilized for mask inspection in a photomask inspection system, although this is not limited to this configuration. In other words, not all sections of the image sensor are then fully utilized for the imaging performance of the image sensor. Therefore, in one embodiment of the invention, unused sections of the image sensor—those not used for mask inspection in a photomask inspection system—can be used for energy monitoring of the incident light, particularly EUV light. In other words, the image sensor can include energy monitoring sections for monitoring the energy of the incident light.

[0038] A calibrated photodiode can be arranged within the illumination area of ​​the camera housing. Preferably, the image sensor and the photodiode are arranged in a plane perpendicular to the axis of incidence of the EUV light incident on the illumination area. The signals from the calibrated photodiode can be used to calibrate the image sensor signals and to monitor the energy of the incident light.

[0039] The invention also relates to a method for testing a camera, wherein the camera comprises a camera housing and a vacuum flange formed on the camera housing. The vacuum flange is configured to attach the camera to a vacuum chamber. The camera housing carries an image sensor. The image sensor comprises an image sensor surface layer, and a first collection plate comprises a first collection plate surface layer, wherein the first collection plate is designed to collect EUV-induced contaminants such as particles and emissions caused by exposure of the image sensor to EUV light in the test system. The first collection plate surface layer corresponds to the image sensor surface layer, such that the composition of the image sensor surface layer is identical to the composition of the first collection plate surface layer.The process includes a preparation phase in which the image sensor surface layer and the first collection plate surface layer are exposed to a vacuum, an exposure phase in which the image sensor surface layer and the first collection plate surface layer are exposed to EUV light, and an evaluation phase in which the first collection plate surface layer is examined.

[0040] The vacuum can be created within a vacuum housing in such a way that the image sensor and the first collection plate are exposed to the vacuum. For this purpose, the camera housing can be attached to a vacuum chamber for forming the vacuum housing using the vacuum flange.

[0041] A purge gas can be introduced into the test system in such a way that the image sensor and the first collecting plate are exposed to the purge gas.

[0042] Creating the vacuum and introducing the purge gas can be done in a preparation phase before the exposure phase.

[0043] During a cleaning phase, the purge gas can be mixed with a diluent gas. The gas mixture can then be extracted from the test system.

[0044] During the evaluation phase, before the surface layer of the first collection plate is examined, the first collection plate can be removed from the camera.

[0045] If the testing system includes a second collection plate, process steps that apply to the first collection plate can also be applied to the second collection plate.

[0046] The exposure phase can last at least one day, preferably at least one month, even more preferably at least one year.

[0047] The disclosure includes further developments of the method with features described in connection with the testing system according to the invention.

[0048] The invention is described below by way of example using advantageous embodiments with reference to the accompanying drawings. Figures: Fig. 1: Schematic representation of a photomask inspection system; Fig. 2: Schematic representation of a photomask; Fig. 3: Top view of an embodiment of a testing system; Fig. 4: Side view of the test system of Fig. 3; Fig. 5: Testing system according to the invention, comprising a vacuum chamber; Fig. 6: Testing system according to the invention, comprising a modular chamber; Fig. 7: Image sensor of a testing system according to the invention; Fig. 8-9: Alternative designs of an image sensor; Fig. 10: Example of the use of the image sensor from Fig. 9; Fig. 11: Alternative embodiment of a testing system according to the invention.

[0049] A photomask inspection system, as in Fig. 1 shown, can be used for the inspection of microlithographic photomasks 17.

[0050] The microlithographic photomasks 17 are generally intended for use in a microlithographic projection illumination system (not shown). In the microlithographic projection illumination system, the photomask 17 is illuminated with extreme ultraviolet (EUV) radiation with a wavelength of, for example, 13.5 nm to project a pattern formed on the photomask 17 onto the surface of a lithographic object in the form of a wafer. The wafer is coated with a photoresist that reacts to the EUV radiation. The photomask inspection system is used to examine whether the photomask meets the specifications and is free of contaminants.

[0051] The photomask 17 can have an aspect ratio between 1:1 and 1:3, preferably between 1:1 and 1:2, and even more preferably between 1:1 and 1:2. The photomask 17 can be substantially rectangular in shape. The photomask 17 can preferably be 5 to 7 inches (12.7 to 17.78 cm) long and wide, and more preferably 6 inches (15.24 cm) long and wide. Alternatively, the photomask 17 can also be 5 to 7 inches (12.7 to 17.78 cm) long and 10 to 14 inches (25.4 to 35.56 cm) wide, and preferably 6 inches (15.24 cm) long and 12 inches (30.48 cm) wide.

[0052] In the photomask inspection system according to Fig. In Figure 1, the photomask 17 is arranged such that an EUV beam 15 emitted by an EUV light source 14 is directed onto the photomask 17 via an illumination system 16. Using the illumination system 16, the EUV radiation is shaped into a beam that serves to illuminate an inspection field 20 on the surface of the photomask 17 with uniform intensity. The inspection field 20, which is small in relation to the surface of the photomask 17, is in Fig. Figure 2 is shown in a non-scale representation. For example, the illuminated area 20 can have a size of 0.5 mm x 0.8 mm. A field stop is arranged in the illumination system 16 to limit the illuminated area to the examination field 20 on the surface of the photomask 17. Using an XY positioner 37, the photomask can be moved in the XY plane to bring different examination fields 20 into the area of ​​the EUV beam path.

[0053] The EUV beam 15 reflected by the photomask 17 passes through a projection optic 22 to an EUV camera 23, which is equipped with an image sensor 24. The projection optic maps the inspection field 20 of the photomask 17 onto the image sensor 24 of the EUV camera 23. The EUV light source 14, the illumination system 16, the photomask 17, the projection optic 22, and the EUV camera 23 are arranged in a vacuum housing 40, which is maintained under negative pressure during operation of the inspection system. The EUV camera 23 includes a camera housing 25 in which the image sensor 24 is located. A rear section of the camera housing 25 protrudes from the vacuum housing 40, while the image sensor 24 is exposed to the vacuum within the vacuum housing 40. Accordingly, the camera housing 25 forms a section of the vacuum housing 40 and is subject to the same pressure difference as other sections of the vacuum housing.

[0054] The EUV light source 14 is a plasma light source in which an EUV beam with a wavelength of 13.5 nm is emitted from a plasma. Tin or xenon are media that can be used to generate a plasma suitable for emitting such an EUV beam. To generate the plasma, a droplet of the medium can be exposed to a laser beam.

[0055] The mirrors of the illumination system 16 and the mirrors of the projection optics 22 are designed as EUV mirrors, exhibiting a particularly high reflectivity for EUV beams. The optical surface of the EUV mirrors can be formed by a highly reflective coating. This can be a multilayer coating, in particular a multilayer coating with alternating layers of molybdenum and silicon. With such a coating, approximately 70% of the incident EUV beam can be reflected. In the case of a so-called grazing mirror, the optical surface can consist of a ruthenium layer.

[0056] The projection optics 22 have a magnification factor of more than 100. In order to fully capture the image generated by the examination field 20 of the photomask 17, the area of ​​the image sensor 24 is larger than the area of ​​the examination field 20, corresponding to the magnification factor. For example, the image sensor 24 can have dimensions on the order of 100 mm to 200 mm.

[0057] During the process, the EUV light 15 damages the surface of the image sensor 24, causing particles from the image sensor surface layer to contaminate the image sensor 24 itself, as well as other parts of the photomask inspection system 16, 22. To counteract this, the vacuum housing 40 is purged with hydrogen as a purge gas. While the purge gas helps against the EUV-induced contamination, it also removes surface layers from components of the inspection system, such as the image sensor 24. The image sensor 24 is subject to outgassing effects caused by the vacuum in the vacuum housing 40 and by the purge gas.

[0058] Fig. 3 and Fig. Figure 4 shows a test system according to the invention for testing an EUV camera 23. The test system comprises an EUV camera 23, a flat first collection plate 101, and a flat second collection plate 201. The EUV camera 23 has a camera housing 25 and a vacuum flange 31 formed on the camera housing 25. The vacuum flange 31 is configured so that the EUV camera 23 can be attached to a vacuum chamber 41. The camera housing 25 carries an image sensor 24, the first collection plate 101, and the second collection plate 201. Since the camera 23 is an EUV camera, the image sensor 24 is sensitive to EUV light.

[0059] The image sensor 24 comprises an image sensor surface layer 28, the first collection plate comprises a first collection plate surface layer 102, and the second collection plate comprises a second collection plate surface layer 202. The first collection plate surface layer 102 corresponds to the image sensor surface layer 28. The image sensor surface layer 28 and the first collection plate surface layer 102 both consist of back-thinned silicon doped with boron implants. The second collection plate surface layer 202 is a ruthenium layer deposited on a substrate and configured to be a mirror surface layer, i.e., a material surface layer that is used in the projection mirrors of the projection optics 22 in the inspection system according to Fig. 1 is used.

[0060] During an exposure phase, higher EUV intensities are used in the test system for a shorter period of time than in the inspection system ( Fig. 1) to predict the long-term behavior of the camera. Even if the exposure period is shorter than the lifespan of a camera in an inspection system, it can still last a year or more.

[0061] In the Fig. 3 and Fig. In the embodiment shown in Figure 4, the first collection plate 101 and the second collection plate 201 capture EUV-induced contaminants such as particles and emissions caused by the exposure of the image sensor 24 to EUV light. Since the surface layer 102 of the first collection plate corresponds to the surface layer 28 of the image sensor, the image sensor surface layer 28 is present twice in the test system. Therefore, thanks to the first collection plate 101, the image sensor surface layer 28 can be evaluated independently of the image sensor 24 itself.

[0062] The test system includes an evaluation unit 27 for reading and analyzing the electrical signals of the image sensor 24. For this purpose, the evaluation unit 27 is electrically connected to the image sensor 24.

[0063] The vacuum flange 31 encloses an illumination area 32 on the camera housing 25. During the exposure phase, the illumination area 32 is illuminated with EUV light. The image sensor 24 and both the first and second collection plates 101, 201 are located within the illumination area 32 and are therefore illuminated with EUV light during the exposure phase.

[0064] The image sensor 24 and both the first and second collection plates 101, 201 are arranged in a plane 33 that is perpendicular to the axis of incidence of the EUV light incident on the illumination area 32. Therefore, both the image sensor surface layer 28 and the first and second collection plate surface layers 102, 202 are exposed to the same EUV light intensity.

[0065] The first and second collection plates 101, 201 are attached to the camera housing by means of a detachable connection. In the embodiment shown, the detachable connection is an EUV-resistant adhesive.

[0066] During the evaluation phase, no EUV light is active; therefore, the illumination area is not irradiated with EUV light. The first and second collection plates 101, 201 are removed from the camera housing 25 by loosening the adhesive bond. Subsequently, the surface layers 102, 202 of the first and second collection plates are analyzed separately from the camera 23 using XPS, i.e., a surface analysis method.

[0067] As in Fig. As shown in Figure 5, the test system according to one embodiment comprises a vacuum chamber 41, wherein the camera 23 is attached to the vacuum chamber 41 by means of the vacuum flange 31. The vacuum chamber 41 and the camera housing 25 together form a vacuum housing 40. The vacuum chamber includes means for generating a vacuum within the vacuum housing 40. The image sensor 24 and both collection plates 101, 201 are exposed to the vacuum within the vacuum housing 40, i.e., there is a pressure difference between the camera housing 25 and the external environment. An EUV light source 14 is arranged inside the vacuum housing 40. The EUV light source 14 has a line of sight to the illumination area 32, which is deflected by several projection mirrors (not shown) that are also arranged within the vacuum chamber 41. The EUV light arriving at the illumination area illuminates the illumination area 32 uniformly.

[0068] Fig. Figure 6 shows another embodiment of the test system. A modular chamber 51 is arranged between the camera 23 and the vacuum chamber 41. The modular chamber 51 is attached to the vacuum chamber 41 by a vacuum flange 52, while the camera housing 25 is attached to the modular chamber 51 by its vacuum flange 31. The vacuum chamber 41, the modular chamber 51, and the camera housing 25 form a vacuum enclosure 40, meaning that there is a pressure differential between the modular chamber 51 and the camera housing 25 and the external environment. The EUV light from the EUV light source 14 is directed through the modular chamber 51 onto the camera 23.

[0069] A first gas inlet 53 is arranged in the modular chamber 51. During the exposure phase, hydrogen is introduced as a purge gas via the modular chamber 51 into the vacuum housing 40 to create a purge gas environment. The camera 23 is exposed to a purge gas environment that corresponds to the purge gas environment in the inspection system according to Fig. 1 corresponds to.

[0070] A second gas inlet 54 is arranged in the modular chamber 51 to introduce nitrogen as a dilution gas into the vacuum housing 40 during a cleaning phase. The nitrogen dilutes the hydrogen inside the vacuum housing 40 to a concentration that can be safely discharged.

[0071] To remove gas from the vacuum housing 40, a first and a second gas outlet 55, 56 are arranged in the modular chamber 51. In one step during the cleaning phase, the vacuum housing 40 is purged with XCDA by rapidly introducing and removing the gas through all gas inlets and outlets.

[0072] An adapter plate 57 is arranged between the modular chamber 51 and the vacuum chamber 41, i.e., between the EUV light source 14 and the image sensor 24 on the camera housing 25. The adapter plate 57 includes a pinhole aperture, meaning that only a certain portion of the EUV light passes through the adapter plate 57 to the image sensor 24.

[0073] According to the in Fig. In the embodiment shown in 7, the image sensor 24 consists of a single sensor 60. Fig. Figure 8 shows an embodiment in which the image sensor 24 consists of several partial sensors 61 arranged in a matrix arrangement. Fig. Figure 9 shows an embodiment in which the image sensor 24 consists of several sub-sensors 62 arranged in a puzzle configuration. The sub-sensors 62 are arranged such that adjacent sub-sensors 62 are vertically offset from one another, forming steps 63 within the arrangement. Fig. Figure 10 shows the puzzle arrangement according to Fig. 9 and arranges the active area 71 of the image sensor 24, which is actually used for imaging. The sections 70 outside the active area 71 do not contribute to the imaging performance but serve to monitor the energy of the incident EUV light. The sections 70 are referred to as energy monitoring sections.

[0074] Fig. Figure 11 shows a further embodiment of the test system in which the photodiodes 80 are arranged in the illumination area 32 near the image sensor 24. The photodiodes 32 are arranged on the plane 33 ( Fig.4) arranged to be exposed to the same EUV light intensity as the image sensor 24 and the collection plates 101, 201. The photodiodes 80 are calibrated before being inserted into the camera 23. Therefore, the signals from the calibrated photodiodes 80 are used to calibrate the signals of the image sensor 24 and to monitor the incident EUV light intensity.

Claims

[1] An inspection system for a camera, comprising the camera (23) and a first capture plate (101), wherein the camera (23) has a camera housing (25) and a vacuum flange (31) formed on the camera housing (25), wherein the vacuum flange (31) is configured to attach the camera (23) to a vacuum chamber (41), wherein the camera housing (25) carries an image sensor (24), wherein the image sensor (24) comprises an image sensor surface layer (28), wherein the first capture plate (101) comprises a first capture plate surface layer (102), wherein the first capture plate (101) is configured to capture EUV-induced contaminants such as particles and emissions caused by exposure of the image sensor (24) to EUV light in the inspection system, and wherein the first capture plate surface layer (102) corresponds to the image sensor surface layer (28),so that the composition of the image sensor surface layer (28) is identical to the composition of the first capture plate surface layer (102)., [2] The inspection system according to claim 1, wherein the camera housing (25) supports the first collecting plate (101). [3] The testing system of claim 1 or 2, comprising a second collecting plate (201), wherein the second collecting plate (201) comprises a second collecting plate surface layer (202). [4] The test system of claim 3, wherein the second trap plate surface layer (202) is a ruthenium layer. [5] The inspection system according to claim 3 or 4, wherein the camera housing (25) supports the second collecting plate (201). [6] Test system according to one of the preceding claims, comprising an evaluation unit (27) for reading out a signal from the image sensor (24). [7] Test system according to one of the preceding claims, comprising a vacuum chamber (41), wherein the camera housing (25) and the vacuum chamber (41) form parts of a vacuum housing (40), and wherein a pressure difference is provided between the interior of the vacuum housing (40) and an external environment. [8] The inspection system of claim 7, comprising an EUV light source (14) disposed inside the vacuum enclosure (40) and having a line of sight to an illumination region (32) for illuminating the image sensor (24) and the first capture plate (101) with EUV light. [9] A test system according to any one of the preceding claims, comprising a first gas inlet (53) for introducing a purge gas and exposing the image sensor (24) and the first collecting plate (101) to the purge gas, and a first gas outlet (55) for discharging gas. [10] Test system according to claim 9, wherein the purge gas is hydrogen and / or helium. [11] Test system according to claim 9 or 10, comprising a second gas inlet (54) for introducing a diluent gas, wherein the diluent gas is nitrogen or an inert gas. [12] Test system according to one of claims 7 to 11, comprising a modular chamber (51) arranged between the vacuum chamber (41) and the camera housing (25) and forming part of the vacuum housing (40). [13] The testing system of claim 12, wherein the first gas inlet (53) and the second gas inlet (54) are disposed in the modular chamber (51). [14] Inspection system according to one of claims 8 to 13, comprising an adapter plate (57) for providing illumination options, wherein the adapter plate (57) comprises a pinhole or is configured for dark field imaging or is configured for white field imaging. [15] Test system according to one of the preceding claims, wherein the image sensor (24) consists of a single sensor (60) or of several sub-sensors in a matrix arrangement (61) or of several sub-sensors in a puzzle arrangement (62). [16] Test system according to one of claims 6 to 15, comprising a calibrated photodiode (80) for calibrating the signal from the image sensor (24). [17] Test system according to one of the preceding claims, wherein the camera (23) is an EUV camera. [18] A method for testing a camera, wherein the camera (23) comprises a camera housing (25) and a vacuum flange (31) formed on the camera housing, wherein the vacuum flange (31) is configured to attach the camera (23) to a vacuum chamber (41), wherein the camera housing (25) carries an image sensor (24), wherein the image sensor (24) comprises an image sensor surface layer (28), wherein a first collecting plate (101) comprises a first collecting plate surface layer (102), wherein the first collecting plate (101) is configured to collect EUV-induced contaminants such as particles and emissions caused by exposure of the image sensor (24) to EUV light in the test system, wherein the first collecting plate surface layer (102) corresponds to the image sensor surface layer (28) such that the composition of the image sensor surface layer (28) corresponds to the composition of the first Collecting plate surface layer (102) is identical, with a preparation phase,in which the image sensor surface layer (28) and the first collecting plate surface layer (102) are exposed to a vacuum, an exposure phase in which the image sensor surface layer (28) and the first collecting plate surface layer (102) are exposed to EUV light, and an evaluation phase in which the first collecting plate surface layer (102) is examined.

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