Mask inspection device and method for adjusting a mask inspection device

Abstract

A mask inspection device comprising a vacuum housing (28), an EUV camera (23), and a projection lens (22) arranged inside the vacuum housing (28) for imaging a section (20) of an EUV photomask (17) onto an image sensor (24) of the EUV camera (23). The EUV camera (23) is attached to the vacuum housing (28). The mask inspection device comprises an actuator (50) for adjusting the position of the EUV camera (23), wherein the actuator (50) acts on a transmission element (43) arranged between the vacuum housing (28) and the EUV camera (23). The transmission element (43) translates an actuation path (48) of the actuator (50) into an adjustment path (47) of the EUV camera (23), wherein the actuation path (48) is longer than the adjustment path (47). The invention also relates to a method for adjusting a mask inspection device.

Description

[0001] The invention relates to a mask inspection device and a method for adjusting a mask inspection device.

[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 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 an EUV 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 mask inspection device suitable for photomasks. The mask inspection device comprises a vacuum housing, within which a projection lens defines an imaging beam path extending from the photomask to the image sensor of the EUV camera. DE 10 2008 034 285 A1 discloses an actuator for the high-precision positioning or manipulation of components, in particular optical elements, in projection exposure systems for semiconductor lithography. DE 10 2009 054 868 A1 relates to a method for adjusting a control pressure for an actuating element, in particular for an actuating element of a manipulator. DE 10 2017 200 633 A1 discloses a lithography system comprising: a movable component, in particular a mirror. DE 10 2023 203 796 A1 discloses a vacuum actuator arrangement for a vacuum system, in particular for an EUV lithography system.It has proven useful to design the mask inspection device so that the EUV camera is attached to the vacuum housing. However, this makes it difficult to adjust the mask inspection device to ensure a perfect image of the photomask on the image sensor of the EUV camera.

[0005] The invention is based on the object of presenting a mask inspection device and a method for adjusting a mask inspection device that mitigates the aforementioned disadvantages. This object is achieved by the features of the independent claims. Advantageous embodiments are specified in the subclaims.

[0006] A mask inspection device according to the invention comprises a vacuum housing, an EUV camera, and a projection lens arranged inside the vacuum housing for imaging a section of an EUV photomask onto an image sensor of the EUV camera. The EUV camera is attached to the vacuum housing. The mask inspection device comprises an actuator for adjusting the position of the EUV camera, wherein the actuator acts on a transmission element arranged between the vacuum housing and the EUV camera. The transmission element translates an actuation path of the actuator into an adjustment path of the EUV camera, wherein the actuation path is longer than the adjustment path.

[0007] The invention is based on the realization that it is not entirely easy to adjust the imaging beam path between the photomask and the image sensor of the EUV camera by adjusting optical elements of the projection lens. According to the invention, the imaging beam path can be adjusted by changing the position of the EUV camera relative to the vacuum housing.

[0008] The invention proposes arranging a transmission element between the EUV camera and the vacuum housing so that the actuating force exerted by an actuator can be transmitted to the EUV camera via the transmission element. The transmission element is designed to translate a larger actuating travel of the actuator into a smaller adjustment travel of the EUV camera. In this way, it becomes possible to apply the considerable forces required to move the EUV camera with a small-sized actuator. The transmission element can be supported on the EUV camera and the vacuum housing. When the actuator is actuated, the state of the transmission element can change, thus adjusting the distance between the vacuum housing and the EUV camera.

[0009] The transmission element can be a hydraulic transmission element. The transmission element can have an interior space filled with a hydraulic fluid. The interior space can be defined by an input piston and an output piston, so that a movement of the input piston along an actuation path is transferred via the hydraulic fluid into a movement of the output piston. The interior space can otherwise be sealed, so that the movement of the input piston and the movement of the output piston correspond directly with one another.

[0010] The transmission element can have a transmission ratio of at least 1:10, preferably at least 1:20, more preferably at least 1:50. With such a transmission ratio, the actuating travel of the input piston is at least a factor of 10, 20, or 50 longer than the adjustment travel of the output piston.

[0011] The direction of movement of the output piston can enclose an angle of at least 80°, preferably at least 85°, more preferably at least 89°, with the plane of the EUV image sensor. With such a design, the transmission element can influence the distance between the EUV image sensor and the vacuum housing. The adjustment path of the output piston can enclose an angle of between 30° and 150°, preferably between 60° and 120°, more preferably between 80° and 100°, with the actuation path of the input piston. In this way, the actuation of the transmission element can be facilitated when the available space in the direction of movement of the output piston is limited.

[0012] The transmission element can be designed to act exclusively on pressure. This means that a transmission of tensile forces between the EUV camera and the vacuum housing is not possible. For this purpose, it is advantageous if the weight of the EUV camera acts against the transmission element. The adjustment path of the transmission element can enclose an angle of no more than 10°, preferably no more than 5°, and more preferably no more than 1° with the vertical. The mask inspector device can be designed so that the EUV camera can be lifted off the transmission element without having to loosen any fastening elements between the EUV camera and the transmission element.

[0013] A clean-room atmosphere can be present outside the vacuum housing. Since conventional hydraulic oils pose a risk of contaminating the clean-room atmosphere, an oil-free hydraulic fluid can be used in the transmission element according to the invention. The hydraulic fluid can be water, for example, particularly deionized water.

[0014] The actuator can be designed to exert a force in a linear direction on the transmission element in order to actuate the transmission element. The actuator can comprise a drive motor and a gearbox, wherein the gearbox is designed to convert a rotary movement of the drive motor into a linear movement. The conversion between the rotary movement and the linear movement can take place, for example, via a rack and pinion or via a threaded mechanism. In one embodiment, the actuator is self-locking. This means that the actuator maintains its current position without external energy being supplied to the actuator. In particular, the self-locking effect ensures that the actuator remains in its position when a force is exerted on the actuator via the transmission element.

[0015] The invention encompasses embodiments in which the transmission element is not a hydraulic transmission element. For example, the transmission element may comprise a lever mechanism or a threaded mechanism to effect the transmission.

[0016] The actuator unit comprising the actuator and the transmission element can be designed to exert a force of at least 500 kg, preferably at least 1000 kg, more preferably at least 2000 kg between the vacuum housing and the EUV camera. This value refers to the weight force that a body with the respective mass would exert. The adjustment range provided by the combination of the actuator and the transmission element can, for example, be between 0.05 mm and 0.5 mm, preferably between 0.1 mm and 0.3 mm.

[0017] The mask inspection device can have at least two transmission elements, preferably at least three transmission elements, between the EUV camera and the vacuum housing. The adjustment paths of the transmission elements can be parallel to one another for the multiple transmission elements. In particular, the adjustment path of the transmission elements can be vertical, i.e., parallel to the force of gravity. Each of the transmission elements can be assigned an actuator so that the transmission elements can be operated independently of one another.

[0018] By operating the transmission elements in parallel, the distance between the EUV camera and the vacuum housing can be changed. The angular orientation of the EUV camera relative to the vacuum housing can remain unchanged. If only individual transmission elements are operated, or if several transmission elements are operated in opposite directions, the angular orientation between the EUV camera and the vacuum housing can be changed. The transmission elements can be arranged so that the EUV camera can be tilted in any direction relative to the vacuum housing.

[0019] The mask inspection device can comprise a control unit configured to generate control signals for controlling the actuators. The control unit can be configured to process input variables to generate the control signals for the actuators. The input variables can be manual inputs. It is also possible to process input variables generated in an automatic process. The input variables can be supplied to the control unit via data transmission.

[0020] In one embodiment, the control unit is an element of a closed control loop. In the closed control loop, the control unit can process a measured value of the position of the EUV camera as an input variable. In one embodiment, a measured value of the position relative to the vacuum housing is processed. The measured value can represent the angle between the Z direction and the plane of the image sensor of the EUV camera. The Z direction refers to the direction of the optical axis of the imaging beam path of the projection lens in a section adjacent to the EUV image sensor. The measured value can additionally or alternatively represent the distance between an image plane of the imaging beam path and the position of the image sensor in the Z direction. The measurement can include the position of the EUV camera in one or more degrees of freedom, in particular in six degrees of freedom.In one embodiment, the number of degrees of freedom of the measurement corresponds to the number of degrees of freedom that can be realized with the existing translation elements. Several measured values ​​can be processed as input variables in the control unit, which relate to various parameters of the position of the EUV camera relative to the vacuum housing. The control unit can be designed to determine the control commands for the actuators in such a way that the difference between an actual position represented by the measured values ​​and a target position is reduced. Additionally or alternatively, measured values ​​can also be processed that represent the position of the EUV camera relative to the projection lens. The same specifications can apply to the number of degrees of freedom of the measurement as for a measurement of the position relative to the vacuum housing.

[0021] An adjustment process according to the invention can be performed during the initial commissioning of the mask inspection device in order to adjust the position of the EUV camera relative to the vacuum housing to a baseline state. An adjustment process according to the invention can additionally or alternatively be performed during operation in order to adjust the position of the EUV camera relative to the vacuum housing between a preceding first operating phase and a subsequent second operating phase. Such an adjustment process can be performed during a break in the operation of the mask inspection device or during ongoing operation.

[0022] In one embodiment, the mask inspection device comprises an adjustment device with which the position of the EUV camera relative to the vacuum housing can be changed while the state of the translation element remains unchanged. The adjustment device can have an adjustment range that is greater than the adjustment range of the translation element. The adjustment range of the adjustment device can, for example, be between 0.5 mm and 2 mm. The adjustment device can be used during the initial commissioning of the mask inspection device to adjust the position of the EUV camera relative to the vacuum housing. The translation elements according to the invention can be used to adjust the position of the EUV camera relative to the vacuum housing during operation of the mask inspection device.This is based on the consideration that during initial commissioning, a larger adjustment range is often required to adjust the mask inspection system than during readjustment during operation.

[0023] The photomask can be arranged within the vacuum housing during the inspection process. The vacuum housing can be designed for a high vacuum. The pressure in the vacuum housing during operation of the mask inspection device can, for example, be between 10 -6 mbar and 10 -9 mbar, preferably between 10 -7 and 10 -8mbar. A pressure difference can be applied across the wall of the vacuum housing, corresponding to the difference between the pressure inside the vacuum housing and atmospheric pressure. The wall of the vacuum housing can be provided with a closable opening designed to allow the photomask to be moved between an interior and exterior space of the vacuum housing.

[0024] The vacuum housing can have an opening to which the EUV camera is connected. The interior of the vacuum housing can be sealed off by the EUV camera so that the same pressure difference exists above the EUV camera as above other areas of the vacuum housing. The opening of the vacuum housing can be vacuum-tightly closed when the EUV camera is attached to the vacuum housing. In this state, the image sensor of the EUV camera can be arranged in the interior of the vacuum chamber. A housing part of the EUV camera can form a section of the wall of the vacuum housing. The vacuum housing can have a flange surrounding the opening to which the EUV camera can be attached. The same pressure difference can exist above the EUV camera as above the vacuum housing. In other words, there is a first area of ​​the EUV camera that is exposed to the interior of the vacuum housing and a second area of ​​the EUV camera that is exposed to the environment.

[0025] A flexible wall section can be formed between the EUV camera and the vacuum housing, which is subject to deformation when the position of the EUV camera is adjusted relative to the vacuum housing. The flexible wall section can form a vacuum-tight seal with the EUV camera housing and a vacuum-tight seal with the vacuum housing. The same pressure difference can be present across the flexible wall section as across other sections of the vacuum chamber wall. The flexible wall section can be configured, for example, as a bellows or a membrane. The transmission element and / or the actuator can be arranged outside the vacuum housing so that these components are not exposed to the vacuum conditions.

[0026] EUV camera components can be tempered to a temperature that differs from the temperature inside the vacuum chamber and from the ambient temperature. In particular, EUV camera components can be cooled to a temperature lower than these temperatures. For the heat transfer required for such temperature control, it is advantageous if the EUV camera housing forms part of the vacuum housing. Externally accessible parts of the camera housing can then be used for heat transfer.

[0027] The mask inspection device can have a frame structure arranged in the vacuum housing, which supports the optical components of the projection lens. The frame structure can be mechanically decoupled from the vacuum housing. This allows the vacuum housing to deform without mechanical stresses being transferred to the frame structure. A connection between the EUV camera and the frame structure can exist via the vacuum housing, to which both the frame structure and the EUV camera are attached. With such a design, it can happen that the EUV camera changes its position relative to the frame structure due to the action of disruptive influences. These can be, for example, thermal influences, dynamic influences, pressure differences, or tolerances. The invention opens up the possibility of compensating for such position changes by adjusting the position of the EUV camera relative to the vacuum housing.

[0028] The mask inspection device can comprise an illumination system with which EUV radiation emanating from an EUV radiation source is directed onto a photomask arranged inside the vacuum housing. The illumination system can be configured to illuminate the photomask with uniform brightness. The optical components of the illumination system can be attached to the frame structure. The projection lens, the illumination system, and the frame structure can thus form a mechanical unit. The projection lens of a mask inspection device is generally designed to generate an enlarged image of a section of a photomask on the EUV image sensor. The magnification factor can be greater than 20, preferably greater than 50, more preferably greater than 100.

[0029] An EUV camera according to the invention can have significantly larger dimensions than commercially available cameras. The weight of the camera can, for example, be higher than 20 kg, preferably higher than 50 kg, more preferably higher than 100 kg. The image sensor of the camera can have the shape 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. An opening in the vacuum housing, through which the EUV camera is attached to the vacuum housing, can have a surface area between 0.2 m 2 and 1 m 2 , preferably between 0.3 m 2 and 0.7 m 2 If the EUV camera is mounted on top of the vacuum housing, the weight of the EUV camera is added to a force exerted by the pressure difference across the camera housing, so that significantly higher forces than the pure weight must be overcome to move the EUV camera.

[0030] The invention relates to a method for adjusting a mask inspection device, wherein the mask inspection device comprises a vacuum housing, an EUV camera, and a projection lens arranged inside the vacuum housing for imaging a section of an EUV photomask onto an image sensor of the EUV camera, and wherein the EUV camera is attached to the vacuum housing. The position of the EUV camera is adjusted using an actuator. The actuator acts on a transmission element arranged between the vacuum housing and the EUV camera. The transmission element translates an actuation path of the actuator into an adjustment path of the EUV camera, wherein the actuation path is longer than the adjustment path.

[0031] The disclosure includes further developments of the method with features described in connection with the mask inspection device according to the invention. The invention includes further developments of the mask inspection device with features described in connection with the method according to the invention.

[0032] 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 a mask inspection system according to the invention; Fig. 2: a schematic representation of a photomask; Fig. 3: a schematic cross-sectional view of an EUV camera; Fig. 4: an aspect of a mask inspection system according to the invention; Fig. 5: a detail from Fig. 4 in a schematic representation; Fig. 6: the view according to Fig. 5 in an alternative embodiment of the invention; Fig. 7, Fig. 8: alternative embodiments of the invention.

[0033] With a Fig. Microlithographic photomasks 17 can be examined using the mask inspection system shown in Figure 1.

[0034] 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 mask inspection system examines whether the photomask meets the specifications and is free of contaminants.

[0035] In the mask inspection system, 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 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 a positioner 29, the photomask 17 can be moved in the horizontal plane to bring various examination fields 20 into the range of the EUV beam path.

[0036] The photomask can, for example, 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.

[0037] 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 images the examination field 20 of the photomask 17 onto the image sensor 24 of the EUV camera 23. The imaging beam path 19 impinges on the image sensor 24 in the Z direction 48. The EUV beam source 14, the illumination system 15, the photomask 17, the projection lens 22, and the image sensor 24 of the EUV camera 23 are arranged in a vacuum chamber 30 surrounded by a vacuum housing 28. During operation of the mask inspection system, a high vacuum exists in the vacuum chamber. The EUV camera 23 comprises a camera housing 25 that supports the image sensor 24. A rear portion 26 of the camera housing 25 protrudes from the vacuum housing 28, while the image sensor 24 is exposed to the vacuum in the vacuum housing 28.The camera housing 25 therefore forms part of the vacuum housing 28 and is exposed to the same pressure difference as other wall areas of the vacuum chamber 30.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] The EUV camera 23 comprises Fig. 3 shows 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 is processed and output as sensor data. Supply lines 38 supply the EUV camera 23 with electrical energy, transmit the sensor data, and operate a cooling device (not shown) that cools components of the EUV camera 23 to a desired temperature.

[0042] 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 establishes a connection between the EUV camera 23 and the vacuum housing 28. In the connected state, the rear side 26 of the camera housing 25, together with the vacuum housing 28, forms a section of the wall of the vacuum chamber 30.

[0043] According to Fig. 4, several actuator units 36 are arranged between the EUV camera 23 and the vacuum housing 28. The space between the flange 31 of the EUV camera 23 and the vacuum housing 28 is sealed by a flexible wall section in the form of a bellows 37. The bellows 37 extends continuously around the circumference of the EUV camera 23. The vacuum housing 28, the camera housing 25, and the bellows 37 form sections in the wall of the vacuum chamber 30, across which the pressure difference between the high vacuum in the interior of the vacuum chamber 30 and the atmospheric pressure in the surrounding area is applied.

[0044] The EUV camera 23 and the vacuum housing 28 are kept at a distance from each other by four actuator units 36, whereby the two in Fig. 4 visible actuator units 36 are spaced apart in the X-direction, and wherein the two in Fig. Four non-visible actuator units 36 are spaced apart from each other in the Y direction. The actuator units 36 can be adjusted independently of each other in length, allowing the distance between the EUV camera 23 and the vacuum housing 28 to be changed. The actuator units 36 are arranged radially outside the bellows 37, so that the actuator units 36 are exposed to atmospheric pressure.

[0045] By appropriately controlling the actuator units 36, the position of the EUV camera 23 can be adjusted relative to the vacuum housing 28. The EUV camera 23 can be tilted around the Y-axis by moving one of the two Fig. 4 visible actuator units 36 is extended and the other is shortened accordingly. The EUV camera 23 can be tilted around the X-axis by one of the two Fig. 4 invisible actuator units 36 are extended and the other is shortened accordingly. The EUV camera 23 can be moved in the Z-direction 48 by extending or shortening all four actuator units 36 together. The actuator units 36 are Fig. 4 control unit 39 not shown.

[0046] The force acting between the EUV camera 23 and the vacuum housing 28 is composed of the weight of the EUV camera 25 and the force resulting from the pressure difference between the vacuum pressure inside the vacuum chamber 30 and atmospheric pressure. The force resulting from the pressure difference significantly outweighs the weight, resulting in a total force equivalent to a weight of several tons. The entire force is transmitted via the actuator units 36. If the position of the EUV camera 23 relative to the vacuum housing 28 is to be changed, the actuator units 36 must overcome this force.

[0047] According to Fig. 5, an exemplary actuator unit 36 ​​comprises an actuator 50 and a transmission element 43. The transmission element 43 has a transmission ratio of more than 1:100, so that a large actuation path 48 of the actuator 50 results in a small adjustment path 47 of the EUV camera 23. Conversely, a small force of the actuator 50 is sufficient to overcome the considerable force acting between the EUV camera 23 and the vacuum housing 28.

[0048] The transmission element 43 has an interior space 49 filled with a hydraulic fluid in the form of deionized water. The otherwise completely enclosed cavity 49 is defined by a small-diameter input piston 46 and a large-diameter output piston 45. The input piston 46 is coupled to the actuator 50, and the output piston 45 is coupled to the EUV camera 23. If the input piston 46 is pushed into the interior space 49, the output piston 45 moves upward, lifting the EUV camera 23.

[0049] The actuator 50 comprises a spindle mechanism with a spindle sleeve 52 and a spindle rod 51. A drive motor 44 drives a rotary motion of the spindle rod 51, which is converted into a linear motion by a threaded engagement with the spindle sleeve 52. The distal end of the spindle rod 51 acts on the input piston 46. The spindle mechanism is self-locking, so that the spindle mechanism holds the input piston 46 in its position without the drive motor 44 exerting any force.

[0050] In the alternative embodiment of an actuator unit 36 ​​in Fig. 6, the transmission element 43 comprises a lever arm 54 resting on a fulcrum 55. A roller 56 is arranged at a distal end of the lever arm 43, which rests against the EUV camera 23 from below. The opposite proximal end of the lever arm 54 is connected to the drive motor 44 of the actuator 50 via a pulley 53. If the pulley 53 is retracted by actuating the drive motor 44, the EUV camera 23 is raised via the roller 56. Such a lever mechanism is also suitable for overcoming the considerable forces between the EUV camera 23 and the vacuum housing 28.

[0051] In Fig. Figure 7 shows a variant in which the EUV camera 23 is equipped with a plurality of distance sensors 41. The distance sensors 41 are designed to measure the distance to targets 40 attached to the projection lens 22. The measured values ​​from the distance sensors 41 are processed in the control unit 39 to determine whether the EUV camera 23 is in the correct position relative to the projection lens 22. If this is not the case, the control unit 39 sends control commands to the actuators 36 so that the difference between the actual position determined by the distance sensors 41 and a desired position of the EUV camera 23 is reduced. The distance sensors 41, the control unit 39, and the actuators 36 are elements of a closed control loop. The control loop is active during operation of the mask inspection system, so that the position of the EUV camera 23 is continuously adjusted to the current conditions.

[0052] In the embodiment according to Fig. 8, several spacer disks 42 are arranged between each of the actuator units 36 and the vacuum housing 29. During initial commissioning of the mask inspection device, the number of spacer disks 42 is individually selected for each of the actuator units 36 to achieve a basic setting in which the EUV camera 23 has approximately the correct alignment relative to the projection lens 22. Further fine adjustment is performed during operation via the actuator units 36.

Claims

[1] Mask inspection device, comprising a vacuum housing (28), an EUV camera (23) and a projection lens (22) arranged inside the vacuum housing (28) for imaging a section (20) of an EUV photomask (17) onto an image sensor (24) of the EUV camera (23), wherein the EUV camera (23) is attached to the vacuum housing (28), further comprising an actuator (50) for adjusting the position of the EUV camera (23) and a transmission element (43) arranged between the vacuum housing (28) and the EUV camera (23), wherein the actuator (50) acts on the transmission element (43), wherein the transmission element (43) translates an actuation path (48) of the actuator (50) into an adjustment path (47) of the EUV camera (23), and wherein the actuation path (48) is longer than the adjustment path (47). [2] Mask inspection device according to claim 1, wherein the transmission member (43) has a transmission ratio of at least 1:10, preferably of at least 1:20, more preferably of at least 1:

50. [3] Mask inspection device according to claim 1 or 2, wherein the transmission member (43) is a hydraulic transmission member. [4] Mask inspection device according to claim 3, wherein the transmission member (43) comprises an input piston (46) and an output piston (45) and wherein the actuating path (48) of the input piston (46) encloses an angle between 30° and 150° with the adjustment path (47) of the output piston (45). [5] Mask inspection device according to claim 3 or 4, wherein the hydraulic fluid of the transmission member (43) is an oil-free hydraulic fluid. [6] Mask inspection device according to one of claims 3 to 5, wherein the hydraulic fluid of the transmission member (43) is deionized water. [7] Mask inspection device according to one of claims 1 to 6, wherein the transmission member (43) is designed to act exclusively on pressure. [8] Mask inspection device according to one of claims 1 to 7, wherein the direction of the adjustment path (47) encloses an angle of not more than 10° with the vertical, which is parallel to the force of gravity. [9] Mask inspection device according to one of claims 1 to 8, wherein a clean room atmosphere is present outside the vacuum housing (28). [10] Mask inspection device according to one of claims 1 to 9, wherein the actuator (50) is self-locking. [11] Mask inspection device according to one of claims 1 to 10, wherein the adjustment path (47) of an actuator unit (36) comprising the transmission element (43) and the actuator (50) is between 0.05 mm and 0.5 mm. [12] Mask inspection device according to claim 11, wherein the actuator unit (36) is designed to exert a force of at least 500 kg between the vacuum housing (28) and the EUV camera (23). [13] Mask inspection device according to one of claims 1 to 12, comprising at least two translation elements (43) between the EUV camera (23) and the vacuum housing (28). [14] Mask inspection device according to claim 13, wherein the adjustment paths (47) of the transmission members (43) are parallel to each other. [15] Mask inspection device according to claim 13 or 14, wherein the transmission members (43) can be actuated independently of one another. [16] Mask inspection device according to one of claims 1 to 15, wherein the same pressure difference is present above the EUV camera (23) as above the vacuum housing (28). [17] Mask inspection device according to one of claims 1 to 16, wherein a flexible wall section (37) is formed between the EUV camera (23) and the vacuum housing (28), which is subjected to deformation when the position of the EUV camera (23) is adjusted relative to the vacuum housing (28). [18] Mask inspection device according to one of claims 1 to 17, wherein the transmission element (43) and / or the actuator (50) are arranged outside the vacuum housing (28). [19] A method for adjusting a mask inspection device, wherein the mask inspection device comprises a vacuum housing (28), an EUV camera (23) and a projection lens (22) arranged inside the vacuum housing (28) for imaging a section (20) of an EUV photomask (17) onto an image sensor (24) of the EUV camera (23), wherein the EUV camera (23) is attached to the vacuum housing (28), wherein the position of the EUV camera (23) is adjusted by an actuator (50), wherein the actuator (50) acts on a transmission element (43) arranged between the vacuum housing (28) and the EUV camera (23), wherein the transmission element (43) translates an actuation path (48) of the actuator (50) into an adjustment path (47) of the EUV camera (23), and wherein the actuation path (48) is longer than the adjustment range (47).

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