Transport and test system for a camera, method for testing a camera

Abstract

A transport and test system for a camera (23), comprising the camera (23), a camera cover (33), and a vacuum connection (35). The camera (23) includes a camera housing (25) and an image sensor (24) arranged on the camera housing (25). A vacuum flange (31) for connection to a vacuum housing is formed on the camera housing (25). The camera cover (33) has a mating flange (34) that fits the vacuum flange (31). In a connected state, the camera (23), the camera cover (33), and the vacuum connection (35) form a camera unit (38) that vacuum-tightly encloses an interior space (39), so that a vacuum can be applied to the interior space (39) via the vacuum connection (35). The invention also relates to a method for testing a camera.

Description

[0001] The invention relates to a transport and test system for a camera and a method for testing a camera.

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

[0003] To ensure high-quality images on the lithographic object, the photomask must be dimensionally accurate and free from contamination. Photomasks are commonly inspected before use in a microlithographic projection exposure system or during downtime. For this purpose, an aerial image of the photomask or a section of the photomask is created, in which the photomask is imaged not onto a lithographic object but onto an EUV image sensor of a camera. Based on the image onto the EUV image sensor, an assessment can be made as to whether the photomask is free of defects and contamination.

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

[0005] CN 1 12 770 039 A discloses a vacuum-tight housing of a scientific SCMOS camera with cooling.

[0006] KR 10 1 629 838 B1 relates to a camera module inspection device and an associated control method.

[0007] Before the installation of a photomask inspection system, the camera is transported separately from other components of the inspection system. Transport can occur, for example, from the camera's manufacturing site to the inspection system's manufacturing site, or from the inspection system's manufacturing site to the site where the inspection system will be commissioned. There is a risk that the EUV camera will be damaged during such transport. It is desirable to be able to test the functionality of an EUV camera before or after transport. However, it is not easy to test the functionality of the EUV camera without the testing process itself being associated with a risk of damage to the EUV camera.

[0008] The invention is based on the object of presenting a transport and testing system for a camera, as well as a method for testing a camera, which mitigate these problems. This object is achieved by the features of the independent claims. Advantageous embodiments are specified in the subclaims.

[0009] A transport and testing system for a camera according to the invention comprises the camera, a camera cover, and a vacuum connection. The camera comprises a camera housing and an image sensor arranged on the camera housing, wherein the image sensor is sensitive to EUV radiation. A vacuum flange is formed on the camera housing and is intended for connection to a vacuum housing. The camera cover has a mating flange that fits the vacuum flange. When connected, the camera housing, the camera cover, and the vacuum connection form a camera unit that encloses an interior space in a vacuum-tight manner, so that a negative pressure can be applied to the interior space via the vacuum connection.

[0010] By creating a vacuum-tight seal between the camera and the camera cover, it is possible to bring the camera into a state that ensures that the camera components adjacent to the interior are not affected by environmental influences during transport. The vacuum connection can be used to create a negative pressure in the interior of the camera unit, making it possible to perform certain tests on the camera without having to open the camera unit. For example, it is possible to test whether the camera unit is sufficiently leak-tight and whether the sensor values ​​output by the camera change when the pressure inside the camera unit is reduced from atmospheric pressure to a vacuum. Ideally, the camera unit can remain closed throughout the entire transport process, from the camera's manufacturing location to its installation in the inspection system, despite interim functional tests.This reduces the risk of damage to the camera during transport.

[0011] The camera is an EUV camera that incorporates an image sensor sensitive to EUV radiation. The EUV camera can be used in an inspection system for mask inspection. In such an inspection system, the photomask is typically inspected under vacuum conditions. The camera cover is detachably connected to the camera in the connected state, allowing it to be easily separated from the camera. When the camera is used in the inspection system (the camera's operational state), the camera cover is separated from the camera.

[0012] The camera can be designed to be connected to an opening of a vacuum housing via the vacuum flange, so that the image sensor is exposed to the vacuum conditions and the outside of the camera housing is outside the vacuum. With such a use, a pressure gradient exists across the camera housing during operation. The camera housing should be vacuum-tight so that it can withstand the pressure gradient. The vacuum flange of the camera housing can be designed to match a flange of the vacuum housing. The vacuum flange of the camera housing can be equipped with a circumferential sealing ring so that the vacuum housing is sealed at the transition to the vacuum flange of the camera housing. In one embodiment, the vacuum flange comprises two sealing rings arranged one behind the other in the direction of the pressure difference.

[0013] A camera specification may be specified that sets limits for outgassing to which camera components are subject when exposed to a vacuum. The camera may be designed to meet the camera specification.

[0014] The camera unit formed for transport and testing of the camera, consisting of the camera and the camera cover, can be vacuum-tight enough to create a pressure gradient between the exterior and interior of the camera unit that corresponds to the pressure gradient during subsequent camera operation. Relative to atmospheric pressure in the exterior, the camera unit can be designed for an interior pressure of between 10 -3 mbar and 10 -9 mbar. In one embodiment, the camera unit is designed for a high vacuum between 10 -6 mbar and 10 -9 mbar.

[0015] The vacuum port can be equipped with a valve that can be switched between an open and a closed state. When the valve is open, the vacuum port forms a passage between the interior and exterior of the camera unit. When closed, the valve is just as sealed as the rest of the camera unit. The vacuum port can be formed in the camera cover. It is also possible for the vacuum port to be part of the camera.

[0016] The testing and transport system according to the invention can comprise a vacuum pump designed to create the desired vacuum in the interior of the camera unit. An inlet opening of the vacuum pump can be designed to be connected to the vacuum connection of the camera unit. The camera unit can be tested for leaks by using the vacuum pump to create a negative pressure in the interior of the camera unit and then closing a valve arranged between the vacuum pump and the interior. This can be the valve of the vacuum connection or a second valve. It can be measured how long the camera unit maintains the negative pressure after the valve has been closed. For this purpose, the testing and transport system can comprise a pressure sensor with which the pressure in the interior of the camera unit is measured. The pressure sensor can be arranged between the valve, which is closed after evacuation, and the vacuum connection of the camera unit.

[0017] The camera cover can be a closed cover so that it is dark inside the camera unit. In such a case, some of the camera's functions can be tested. A dark image can be generated to determine which sensor values ​​the camera outputs when no light hits the image sensor. In one embodiment, a first dark image is generated when atmospheric pressure is present inside the camera unit, and a second dark image is generated when negative pressure is present inside the camera unit. The method can be refined by taking further dark images for various intermediate values ​​of the pressure inside the camera unit. In this way, it can be determined how the sensor values ​​output by the camera change depending on the pressure to which the image sensor is exposed.

[0018] Additionally or alternatively, the camera unit can be tested for outgassing into the interior of the camera unit. The transport and test system can include a residual gas analyzer for this purpose. The residual gas analyzer can be connected to the camera unit in such a way that a volume of gas drawn from the interior of the camera is fed to the residual gas analyzer, allowing the residual gas analyzer to analyze the gas composition. Based on the composition of the residual gas, it can be determined whether the outgassing into the interior of the camera unit is below the specified limits.

[0019] In another embodiment, the camera cover is provided with a light passage so that electromagnetic radiation, in particular visible light or UV radiation, can pass between the interior and exterior of the camera. Such a light passage is referred to below as a window. This enables further testing of the camera, in which it is determined which sensor values ​​the camera outputs when different amounts of electromagnetic radiation hit the image sensor. A bright image can be generated in which all pixels of the image sensor are saturated. The test procedure can be refined by directing different amounts of electromagnetic radiation onto the image sensor, which lie between the bright image and the dark image.

[0020] The image sensor is an EUV sensor, which is sensitive to electromagnetic radiation in the extreme ultraviolet spectral range. In the present application, EUV radiation refers to electromagnetic radiation with a wavelength between 5 nm and 30 nm, with 30 nm forming the upper limit of the EUV spectrum. The wavelength of the electromagnetic radiation with which the camera is tested can be at least a factor of 5, preferably at least a factor of 10, larger than the upper limit of the EUV spectrum. In particular, the test can be carried out with light in the near ultraviolet range or in the visible range. This has the advantage that the window, which is a vacuum-tight component of the camera cover, can be made of a conventional light-transmitting material, such as glass, which is opaque to EUV radiation.Unlike EUV radiation, radiation in the visible or near-ultraviolet wavelength range can pass through glass essentially unhindered. It has been shown that EUV sensors are also sensitive to longer-wavelength electromagnetic radiation to a certain extent, and that a statement about the functionality of the image sensor can therefore also be made using longer-wavelength electromagnetic radiation as the measurement radiation.

[0021] The camera unit can be designed so that there is no additional cover between the camera cover window and the camera's image sensor through which the radiation must pass. A propagation path toward the image sensor that is as unobstructed as possible is particularly important in the case of EUV radiation, since material is generally highly absorbent of EUV radiation. A pellicle is not considered a cover within the meaning of this paragraph. A pellicle is a membrane that retains particles and allows EUV radiation to pass through. A pellicle can, for example, be formed as a CNT (carbon nanotube) pellicle.

[0022] The transport and test system can comprise a light source designed to direct light through the window of the camera cover onto the image sensor of the camera when the transport and test system is in a test state. The light source can be embodied as part of a light table. The light table can comprise an upwardly facing cover plate through which the light can pass. The camera test can be carried out by placing the camera unit on the light table. The camera unit can be aligned such that the measuring radiation emitted by a light source of the light table strikes the image sensor through the cover plate of the light table and the window of the camera cover. In one embodiment, the measuring radiation can propagate in a straight line from the light source to the image sensor.

[0023] The camera unit and the light table can be coordinated so that no external light can reach the image sensor. This makes it possible to record a dark image with the image sensor when the light table's light source is turned off.

[0024] The light source of the light table can comprise multiple radiation cores, each emitting measurement radiation when the light source is switched on. The radiation sources can be arranged in an array. In one embodiment, the light source is formed by an array of light-emitting diodes. The cover plate of the light table can have a homogenizing effect on the emitted light, so that the light cones of the individual radiation sources form measurement radiation, thus illuminating the image sensor with uniform brightness.

[0025] The light source can be a calibrated light source, so that a defined relationship exists between the setting to which the light source is set and the actual amount of electromagnetic radiation emitted. For example, the intensity of the emitted radiation can be calibrated to an accuracy of + / - 1%. This allows for direct calibration of the camera, which determines which sensor values ​​the image sensor delivers at which amount of measurement radiation.

[0026] The transport and test system can be used so that immediately after camera production, a camera cover is placed over the vacuum flange of the camera housing to form a vacuum-tight camera unit. This step can take place in a clean room so that the conditions inside the camera unit correspond to the atmosphere in the clean room. Before shipping, the camera manufacturer can perform one or more of the described tests for outgoing inspection. If the camera unit is then transported from the camera manufacturing site to the manufacturing site of the facility in which the camera will later be used, the facility manufacturer can perform one or more of the described tests on the camera without having to open the camera unit. The risk of the camera becoming contaminated as a side effect of the tests performed is thus significantly reduced.

[0027] If the camera is deemed to be satisfactory, it can be transported along with other system components to the site where the system will be erected. Before the camera is installed on the system, further tests can be carried out on the camera. The tests can be of the same scope as those carried out by the system manufacturer or to a lesser extent. Alternatively, the camera unit can be transported directly from the camera manufacturer's site to the site where the system will be erected, and the camera can only be subjected to the required tests there. In both cases, the camera unit can remain continuously closed from the time the camera unit is sealed at the camera manufacturer's site until the time the camera unit is opened again to connect the camera to the system's vacuum housing via the vacuum flange.

[0028] The removable connection between the camera cover and the camera housing can be a screw connection, for example. The screw connection can be established via holes in the vacuum flange of the camera housing, which are also used to connect the camera housing to the housing of the system. The system can be, for example, a photomask inspection system. The camera cover can be designed for reuse. Once the camera cover has been removed from one camera, it is available for later use on another camera. It is also possible for the camera cover to be reused on the same camera, for example, for maintenance purposes.

[0029] During transport, the camera unit is lifted several times. The camera unit can include pivot points that can be accessed with a lifting device. The pivot points can be formed on the camera cover. The camera can be significantly larger than commercially available cameras. The weight of the camera can, for example, be higher than 20 kg, preferably higher than 50 kg, and more preferably higher than 100 kg. The camera's image sensor can be in the form of an approximately rectangular array. One of the edge lengths of the rectangle spanned by the array can, for example, be between 100 mm and 200 mm.

[0030] The inspection system in which the camera of the system according to the invention is used can be designed for inspecting photomasks. The photomask can have an aspect ratio between 1:1 and 1:3, preferably between 1:1 and 1:2, particularly preferably 1:1 or 1:2. The photomask can be substantially rectangular. The photomask can preferably be 5 to 7 inches (12.7 cm to 17.8 cm) long and wide, particularly preferably 6 inches (15.2 cm) long and wide. Alternatively, the photomask can be 5 to 7 inches (12.7 cm to 17.8 cm) long and 10 to 14 inches (25.4 cm to 35.6 cm) wide, preferably 6 inches (15.2 cm) long and 12 inches (30.5 cm) wide.

[0031] The invention also relates to a method for testing a camera, in which the camera comprises a camera housing and an image sensor arranged on the camera housing, the image sensor being sensitive to EUV radiation. A vacuum flange is formed on the camera housing for connection to a vacuum housing. A camera cover, which has a mating flange that fits the vacuum flange, is placed on the vacuum flange, so that the camera and the camera cover form a camera unit that encloses an interior space in a vacuum-tight manner. A negative pressure is applied in the interior space.

[0032] In a further step of the method according to the invention, the composition of a gas volume drawn from the interior can be analyzed. Additionally or alternatively, the dependence of a sensor signal generated by the image sensor on the pressure prevailing in the interior can be examined. Additionally or alternatively, a window can be formed in the camera cover, with light being directed through the window onto the image sensor, and the dependence of a sensor signal generated by the image sensor on the light directed onto the image sensor being examined.

[0033] The disclosure includes further developments of the method with features described in the context of the transport and test system according to the invention. The invention includes further developments of the transport and test system described in the context of the method according to the invention.

[0034] The invention is described below by way of example with reference to advantageous embodiments in the accompanying drawings. They show: Fig. 1: a schematic representation of an inspection system according to the invention; Fig. 2: a schematic representation of a photomask; Fig. 3: a perspective view of an EUV camera according to the invention; Fig. 4: a schematic cross-sectional view of the EUV camera from Fig. 3; Fig. 5: a schematic view from below of the EUV camera from Fig. 4; Fig. 6: a camera unit according to the invention in the open state; Fig. 7: the camera unit Fig. 6 in closed position; Fig. 8: a first embodiment of a transport and test system according to the invention; Fig. 9: a second embodiment of a transport and test system according to the invention.

[0035] With a Fig. Microlithographic photomasks 17 can be examined using the inspection system shown in Figure 1.

[0036] Microlithographic photomasks 17 are generally intended for use in a microlithographic projection exposure system (not shown). In the microlithographic projection exposure system, the photomask 17 is illuminated with extreme ultraviolet radiation (EUV radiation) with a wavelength of, for example, 13.5 nm in order to image a structure 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 inspection system examines whether the photomask meets the specifications and is free of contaminants.

[0037] In the inspection facility, according to Fig. 1, the photomask 17 is arranged such that an EUV beam path 15 emanating from an EUV radiation source 14 is guided onto the photomask 17 via an illumination system 16. The illumination system 16 forms the EUV radiation into a beam bundle, which illuminates an examination field 20 on the surface of the photomask 17 with uniform brightness. The examination field 20, which is small in relation to the area of ​​the photomask 17, is shown in a representation not to scale in Fig. 2. The illuminated area 20 can, for example, have dimensions of 0.5 mm x 0.8 mm. The edge lengths of the photomask 17 can, for example, be between 100 mm and 200 mm. A field stop is arranged in the illumination system 16, with which the illuminated area is limited 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 various examination fields 20 into the range of the EUV beam path.

[0038] The EUV beam path 15 reflected by the photomask 17 continues via a projection lens 22 to an EUV camera 23 equipped with an image sensor 24. The projection lens projects the examination field 20 of the photomask 17 onto the image sensor 24 of the EUV camera 23. The EUV radiation source 14, the illumination system 15, the photomask 17, the projection lens 22, and the EUV camera 23 are arranged in a vacuum housing 40, in which a negative pressure is maintained during operation of the inspection system. The EUV camera 23 comprises a camera housing 25, within which the image sensor 24 is arranged. A rear part 26 of the camera housing 25 protrudes from the vacuum housing 40, while the image sensor 24 is exposed to the vacuum in the vacuum housing 40. The camera housing 25 therefore forms part of the vacuum housing 40 and is exposed to the same pressure difference as other areas of the vacuum housing.

[0039] The EUV radiation source 14 is a plasma radiation source in which EUV radiation with a wavelength of 13.5 nm is emitted from a plasma. Tin is a medium with which a plasma suitable for emitting such EUV radiation can be generated. To generate the plasma, a droplet of the medium can be exposed to a laser beam.

[0040] The mirrors of the illumination system 16 and the mirrors of the projection lens 22 are designed as EUV mirrors, which have a particularly high reflectivity for EUV radiation. 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 radiation can be reflected.

[0041] The projection lens 22 has a magnification factor of more than 100. In order to be able to completely record 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 in accordance with the magnification factor. The image sensor 24 can, for example, have dimensions in the order of 100 mm to 200 mm.

[0042] The EUV camera 23 comprises Fig. 3, Fig. 4, a housing 25 on which the image sensor 24 and an electronics unit 27 are arranged. The electronics unit 27 controls the image sensor 24, and the EUV image data acquired by the image sensor 24 are processed and output as sensor data. A pellicle flange 29 is formed on the housing 25, over which a pellicle 30 is stretched, see Fig. 4. EUV radiation coming from the projection lens 22 passes through the pellicle 30 and strikes the image sensor 24. In the schematic representation of the Fig. Figure 5 shows a view through the pellicle 30 onto the image sensor 24. The pellicle 30 is a very thin membrane made of carbon nanotubes that allows EUV radiation to pass through easily, but impedes the passage of particles. The pellicle 30 ensures that particles contained in the atmosphere of the inspection system cannot settle on the image sensor 24. Particles on the image sensor 24 distort the images recorded from the examination field 20 of the photomask 17.

[0043] A vacuum flange 31 is formed on the camera housing 25, extending continuously around the circumference of the camera housing 25. The vacuum flange 31 is equipped with two circumferential sealing rings 32, which are arranged one behind the other in the direction of the pressure difference across the vacuum flange 31. The camera 23 is screwed to the vacuum housing 40 via the vacuum flange 31. The rear side 26 of the camera housing 25 thus forms a section of the vacuum housing 40.

[0044] The Fig. Figure 3 shows the camera 23 immediately after production at the camera manufacturer. Before the final inspection, the camera manufacturer connects the camera 23 to a camera cover 33, see Fig. 6, Fig. 7. The camera cover 33 comprises a mating flange 34 that fits the vacuum flange 31 of the camera housing 25, via which the camera cover 33 is screwed to the camera housing 25. This creates a camera unit 38 that is vacuum-tight in the same way as the vacuum housing 40 of the inspection system, see Fig. 7. The camera unit 38 forms a transport and test system within the meaning of the invention.

[0045] The camera cover 33 is provided with a vacuum connection 35, through which a negative pressure can be applied in the interior 39 of the camera unit 38. The vacuum connection 35 can be switched between an open and a closed state via a valve 36.

[0046] The sealing of the camera unit 38 takes place in a clean room of the camera manufacturer, so that the conditions in the interior 39 of the camera unit 38 correspond to the atmosphere in the clean room. After the exit inspection, the interior 39 of the camera unit 38 is at atmospheric pressure. In this state, the camera unit 38 is transported to the manufacturing site of the photomask inspection system.

[0047] In Fig. Figure 8 shows a variant in which the transport and test system comprises a vacuum pump 41 and a residual gas analyzer 42. The manufacturer of the inspection system performs an incoming inspection by connecting a vacuum pump 41 to the vacuum connection 35. The valve 36 is opened and the vacuum pump 41 is activated, so that a high vacuum with a pressure of, for example, 10 -7mbar is applied. The valve 36 is closed, and a pressure sensor 48 checks how long it takes for the pressure in the interior 39 of the camera unit 38 to increase. If the pressure increases too quickly, the camera unit 38 is not sufficiently sealed, which means that the camera 23 cannot be used in this state.

[0048] The gas drawn from the interior 39 of the camera unit 38 is fed to a residual gas analyzer 42, where the gas's composition is analyzed. If the gas contains too many foreign substances, it can be concluded that outgassing has occurred from camera components. The camera 23 is then not functioning properly.

[0049] If the camera unit 38 is found to be free of defects during the incoming inspection, it is released for further use, which involves installing the camera 23 in an inspection system for photomasks. The camera unit 38 remains closed for further transport there. The camera unit 38 is opened again for the first time shortly before the camera 23 is installed in the inspection system.

[0050] In Fig. Figure 9 shows an embodiment of a transport and test system in which the camera cover 33 is provided with a window 43 so that light from outside can hit the image sensor 24. The vacuum connection, which is also present, is shown in Fig. 9 not shown. The transport and test system further comprises a light table 44, inside which an array of light-emitting diodes 45 is arranged. During operation of the light table 44, the light-emitting diodes 45 emit light with a wavelength that lies in the short-wave range of visible light. The light table 44 is calibrated so that, for a given setting of the light table 44, the amount of emitted light is defined to within + / -1%.

[0051] The upper surface of the light table 44 is formed by a cover plate 46 made of a translucent material. The cover plate 46 has a homogenizing effect on the light emitted by the LEDs 45, so that the light emerges upward from the cover plate 46 with brightness evenly distributed across the surface.

[0052] The camera unit 38 can be placed with its underside on the end plate 46 of the light table 44. In Fig.Figure 9 shows a state shortly before placement, in which the camera unit 38 is still positioned slightly above the cover plate 46. Ring-shaped pivot points 47 are formed on the camera cover 33, which are engaged with a lifting device (not shown) to position the camera unit 38.

[0053] When the camera unit 38 rests on the end plate 46, light emitted by the LEDs 45 passes through the end plate 46 of the light table 44 and through the window 43 of the camera cover 33 and strikes the image sensor 24 of the EUV camera 23. Since the amount of emitted light is known due to the calibration of the light table 44, the image sensor 24 of the camera 23 can also be calibrated by making a correlation between the sensor data and the setting of the light table.

[0054] If necessary, the test can extend across the full dynamic range of the image sensor 24. For this purpose, the LEDs 45 can initially be switched off, so that the image sensor 24 captures a dark image. The brightness of the LEDs 45 can then be increased in any number of steps until the image sensor 24 is saturated. Although the image sensor 24 is primarily sensitive to EUV radiation, the longer-wavelength light from the LEDs 45 also generates a sensor signal from the image sensor 24, which is why it is possible to perform the image sensor test with visible light.

Claims

[1] Transport and test system for a camera (23), comprising the camera (23), a camera cover (33) and a vacuum connection (35), wherein the camera (23) comprises a camera housing (25) and an image sensor (24) arranged on the camera housing (25), wherein the image sensor (24) is sensitive to EUV radiation, wherein a vacuum flange (31) intended for connection to a vacuum housing is formed on the camera housing (25), wherein the camera cover (33) has a counter-flange (34) matching the vacuum flange (31), wherein in a connected state the camera (23), the camera cover (33) and the vacuum connection (35) form a camera unit (38) which encloses an interior space (39) in a vacuum-tight manner, such that a negative pressure can be applied in the interior space (39) via the vacuum connection (35). [2] Transport and test system according to claim 1, wherein in the connected state the camera cover (33) is detachably connected to the camera (23) and wherein in a use state of the camera (23) the camera cover (33) is separated from the camera (23). [3] Transport and test system according to claim 1 or 2, wherein the vacuum port (35) is formed in the camera cover (33). [4] Transport and test system according to one of claims 1 to 3, comprising a residual gas analyzer (42) to which a quantity of gas sucked in from the interior (39) of the camera unit (38) is supplied. [5] Transport and test system according to one of claims 1 to 4, wherein the camera cover (33) is provided with a window (43). [6] Transport and test system according to claim 5, wherein the window (43) is made of a material that is opaque to EUV radiation. [7] Transport and test system according to claim 5 or 6, comprising a light source (45), wherein the transport and test system is designed for a test state in which light emitted by the light source (45) is guided through the window (43) onto the image sensor (24). [8] Transport and test system according to claim 7, wherein the light emitted by the light source (45) has a wavelength which is at least a factor of 5, more preferably at least a factor of 10, longer than the wavelength at the upper limit of the EUV spectrum. [9] Transport and test system according to claim 7 or 8, wherein the light source (45) is a component of a light table (44) and wherein the light source (45) illuminates an upwardly facing end plate (46) of the light table (44). [10] Transport and test system according to claim 9, wherein the end plate (46) homogenizes the light emitted by the light source (45). [11] Transport and test system according to one of claims 1 to 10, wherein articulation points (47) for a lifting device are formed on the camera cover (33). [12] Transport and test system according to one of claims 1 to 11, wherein the weight of the camera (23) is higher than 20 kg, preferably higher than 50 kg, more preferably higher than 100 kg. [13] A method for testing a camera (23), wherein the camera (23) comprises a camera housing (25) and an image sensor (24) arranged on the camera housing (25), wherein the image sensor (24) is sensitive to EUV radiation, wherein a vacuum flange (31) intended for connection to a vacuum housing is formed on the camera housing (25), wherein a camera cover (33), which has a counter-flange (34) matching the vacuum flange (31), is placed on the vacuum flange (31), so that the camera (23) and the camera cover (33) form a camera unit (38) which encloses an interior space (39) in a vacuum-tight manner, and wherein a negative pressure is applied in the interior space (39). [14] Method according to claim 13, wherein the composition of a gas volume sucked from the interior (39) is analyzed. [15] Method according to claim 13 or 14, wherein the dependence of a sensor signal generated by the image sensor (24) on the pressure present in the interior space (39) is examined. [16] Method according to one of claims 13 to 15, wherein a window (43) is formed in the camera cover (33), wherein light is directed through the window (43) onto the image sensor (24), and wherein the dependence of a sensor signal generated by the image sensor (24) on the light directed onto the image sensor (24) is examined.

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