Mask inspection device and method for adjusting mask inspection device

Abstract

To provide a mask inspection device comprising: a vacuum housing (28); an EUV camera (23); and a projection lens (22) arranged in the interior of the vacuum housing (28) and configured for imaging at least one portion (20) of an EUV photomask (17) onto an image sensor (24) of the EUV camera (23).SOLUTION: The EUV camera (23) is mounted on the vacuum housing (28). The position of the EUV camera (23) is adjustable between a first position and a second position relative to the vacuum housing (28) by use of an adjusting mechanism (33). The invention also relates to a method for adjusting the mask inspection device.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] In microlithography projection exposure apparatus, which are used to manufacture integrated circuits, particularly those with very small structures, photomasks are used that are irradiated with very short-wave extreme ultraviolet radiation (EUV) and imaged onto the lithography object in order to transfer the mask structure onto the lithography object.

[0003] To ensure a high quality of the image formed on the lithography object, the photomask needs to be true to size and not be adversely affected by contaminants. It is known practice to subject the photomask to inspection before operation in a microlithography projection exposure apparatus or during interruptions in operation. For this purpose, a so-called aerial image of a portion of the photomask is generated, in which case the photomask is imaged onto an EUV image sensor rather than onto the lithography object. Using the imaging onto the EUV image sensor as a basis, the photomask can be assessed for defects and contaminants.

[0004] Inspection is typically performed in a mask inspection device suited to the photomask. The mask inspection device includes a vacuum housing in which a projection lens defines an imaging beam path extending from the photomask to the image sensor of the EUV camera. It has proven convenient to design the mask inspection device so that the EUV camera is mounted on the vacuum housing. However, adjusting the mask inspection device to produce a perfectly satisfactory image of the photomask on the sensor of the EUV camera is then not a simple matter. Summary of the Invention

[0005] The present invention is based on the object of providing a mask inspection device and a method for operating a mask inspection device which alleviates the above-mentioned drawbacks. This object is achieved by the features of the independent claims. Advantageous embodiments are specified in the dependent claims.

[0006] A mask inspection device according to the present invention includes a vacuum housing, an EUV camera, and a projection lens disposed within the vacuum housing for imaging a portion of the EUV photomask onto an image sensor of the EUV camera. The EUV camera is mounted on the vacuum housing. The position of the EUV camera is adjustable between a first position and a second position relative to the vacuum housing using an adjustment mechanism.

[0007] The present invention is based on the realization that adjusting the imaging beam path between the photomask and the image sensor of the EUV camera by adjusting the optical elements of the projection lens is not a simple problem. Often, long adjustment travel distances are required, which are not always available within the vacuum housing of the mask inspection device. The present invention instead proposes changing the position of the EUV camera relative to the vacuum housing to adjust the imaging beam path. The position of the EUV camera can be adjusted between multiple discrete positions. It is also possible for the position of the EUV camera to be continuously adjustable between multiple positions.

[0008] The mask inspection device can be designed such that changing the EUV camera between the first position and the second position includes displacement. The displacement refers to a movement that changes the position of the EUV camera relative to the vacuum housing, but the alignment of the EUV camera with respect to the imaging beam path remains unchanged. The displacement causes the center of gravity of the EUV camera to be in a different position.

[0009] Changing the EUV camera between the first and second positions can include a displacement in the Z direction, where the Z direction refers to the direction of the optical axis of the last section of the beam path upstream of the EUV camera. The displacement in the Z direction can be used to compensate for an offset of the EUV camera relative to the focal plane of the imaging beam path.

[0010] Changing the EUV camera between the first and second positions can include a displacement perpendicular to the Z direction, thereby compensating for inaccuracies that result from the imaging path being laterally displaced relative to the image sensor of the EUV camera.

[0011] Additionally or alternatively, the change in position of the EUV camera between the first position and the second position can include tilting the EUV camera relative to the imaging beam path, where the tilt changes the orientation of the EUV camera in space.

[0012] The tilt can be induced about an axis perpendicular to the Z direction. In this way, it is possible to compensate for imaging aberrations caused by the image sensor of the EUV camera not being at the correct angle with respect to the Z direction. In one embodiment, tilt in any direction relative to the Z direction is made possible by allowing the EUV camera to tilt about two mutually orthogonal axes that span a Cartesian coordinate system with respect to the Z direction. Other types of adjustment mechanisms that achieve the same effect are also possible.

[0013] The mask inspection device can be designed such that a change in the position of the EUV camera between a first position and a second position combines a displacement with a tilt. Specifically, a displacement in the Z direction can be combined with a tilt about an axis perpendicular to the Z direction. In one embodiment, the mask inspection device is configured such that the position of the EUV camera is adjustable relative to the vacuum housing in all six degrees of freedom.

[0014] The adjustment mechanism used to adjust the position of the EUV camera relative to the vacuum housing can be designed for manual actuation. In one embodiment, spacer washers located between the EUV camera and the vacuum housing are modified for the adjustment process. Spacer washers can be added or removed, or existing spacer washers can be replaced with other spacer washers. Other adjustment mechanisms designed for manual actuation are also possible. For example, one or more screw mechanisms, toothed rack mechanisms, or similar mechanisms used to mount the EUV camera on the vacuum housing can be adjusted. The available adjustment travel distance can be, for example, 0.1 mm to 2 mm, preferably 0.2 mm to 1 mm.

[0015] The EUV camera can also be mounted to the vacuum housing using one or more actuators. The one or more actuators can be designed to trigger mechanical actions that adjust the position of the EUV camera relative to the vacuum housing in response to received control signals. The available adjustment travel distance can be, for example, 0.1 mm to 2 mm, preferably 0.2 mm to 1 mm. The mask inspection device can include a control unit designed to generate the control signals used to control the actuators.

[0016] The control unit can be designed to process input variables to generate control signals for the actuators. The input variables can be manually entered. It is also possible to process input variables generated by an automatic process. The input variables can be provided to the control unit by data transfer.

[0017] In one embodiment, the control unit is an element of a closed control loop. In the closed control loop, the control unit can process measurements related to the position of the EUV camera as input variables. In one embodiment, measurements related to the position relative to the vacuum housing are processed. The measurements can represent an angle between the Z direction and the plane of the image sensor of the EUV camera. Additionally or alternatively, the measurements can represent a distance between the plane of the imaging beam path and the position of the image sensor in the Z direction. The measurements can include one or more degrees of freedom of the EUV camera position, in particular six degrees of freedom. In one embodiment, the number of degrees of freedom of the measurements corresponds to the number of degrees of freedom of the adjustment mechanism. Multiple measurements related to various parameters of the position of the EUV camera relative to the vacuum housing can be processed as input variables in the control unit. The control unit can be designed to determine control commands for the actuators such that the difference between the actual position represented by the measurements and the target position is reduced. Additionally or alternatively, measurements representing the position of the EUV camera relative to the projection lens can also be processed. The specifications applicable to the number of degrees of freedom of the measurements can be the same as those for the measurements of the position relative to the vacuum housing.

[0018] The adjustment process according to the present invention can be performed during initial startup of the mask inspection device to adjust the position of the EUV camera relative to the vacuum housing to a base state. Additionally or alternatively, the adjustment process according to the present invention can be performed during operation to adjust the position of the EUV camera relative to the vacuum housing between a first operation phase and a subsequent second operation phase. Such an adjustment process can be performed during an interruption in operation for such an inspection instruction or during ongoing operation. Both during initial startup and during operation, the adjustment process can be performed manually or by an actuator.

[0019] In one embodiment, the mask inspection device may include both a manually actuated adjustment mechanism and an actuator controlled by a control signal to adjust the position of the EUV camera relative to the vacuum housing. The manually actuated adjustment mechanism may have an adjustment travel distance longer than that of the actuator. The adjustment travel distance of the manually actuated adjustment mechanism may be, for example, 0.5 mm to 2 mm. The adjustment travel distance of the actuator may be, for example, 0.05 mm to 0.5 mm, preferably 0.1 mm to 0.3 mm. The manually actuated adjustment mechanism may be used during initial startup setup of the mask inspection device to adjust the position of the EUV camera relative to the vacuum housing. The actuator may 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 the adjustment travel distance required to adjust the mask inspection device is often larger during initial startup compared to readjustment during operation. In the case of the actuator, the smaller adjustment travel distance allows for reduced complexity and cost savings.

[0020] The mask inspection device can include a vacuum chamber in which the photomask is placed during the inspection process. The vacuum chamber can be designed for high vacuum. The pressure in the vacuum chamber during operation of the mask inspection device can be, for example, 10 -6 mbar~10 -9 mbar, preferably 10 -7 mbar~10 -8 A pressure difference corresponding to the difference between the pressure inside the vacuum chamber and atmospheric pressure can exist through the wall of the vacuum chamber. The wall of the vacuum chamber can include a closable opening designed to allow the photomask to be changed between the inside and outside of the vacuum chamber.

[0021] The wall of the vacuum chamber can be formed partially or completely by the vacuum housing. In one embodiment, the EUV camera forms part of the wall of the vacuum chamber. This means that the pressure difference that exists across the EUV camera is the same as the pressure difference that exists across other areas of the vacuum housing. To this end, the vacuum housing can have an opening that is 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 located inside the vacuum chamber. A housing portion of the EUV camera can form one section of the wall of the vacuum chamber. The vacuum housing can have a flange that surrounds the opening and onto which the EUV camera can be attached. A pressure difference can exist between the inside of the vacuum housing and the ambient air through the EUV camera.

[0022] A flexible wall section can be formed between the EUV camera and the vacuum housing, and undergoes deformation when the position of the EUV camera is adjusted relative to the vacuum housing. The flexible wall section can terminate in a vacuum-tight manner at the EUV camera housing and can terminate in a vacuum-tight manner at the vacuum housing. A pressure difference existing across the flexible wall section can be the same as a pressure difference existing across other sections of the wall of the vacuum chamber. The flexible wall section can be configured, for example, as a bellows or as a membrane. The adjustment mechanism can be located outside the flexible wall section so that the adjustment mechanism is not exposed to vacuum conditions.

[0023] If the housing of the EUV camera forms part of the wall of the vacuum chamber, a significant force is required to change the position of the EUV camera relative to the vacuum housing. To reduce the required actuation force, the EUV camera can be placed under prestress relative to the vacuum housing, which prestress counteracts the force caused by the vacuum. The prestress can be caused, for example, by a spring element arranged between the EUV camera and the vacuum housing.

[0024] The components of the EUV camera can be temperature regulated from the temperature inside the vacuum chamber and to temperatures deviating from the ambient temperature. In particular, the components of the EUV camera can be cooled to temperatures below these temperatures. For the heat conduction required for such temperature regulation, it is advantageous if the housing of the EUV camera forms part of the vacuum chamber. In that case, parts of the camera housing that are accessible from the outside can be used for heat conduction.

[0025] In another embodiment, the EUV camera is placed inside a vacuum housing. In that case, no significant pressure differential exists across the EUV camera housing. Power lines for the EUV camera can be routed through the vacuum housing. The power lines can be for, for example, supplying voltage to the EUV camera, transmitting electrical signals, and / or conducting heat.

[0026] The supply line may include a section exposed to the vacuum pressure in the vacuum chamber. This section may be located between the vacuum housing and the EUV camera. The supply line must be designed to withstand vacuum conditions, at least in this section, which means in particular that outgassing is within predetermined limits. It is also possible to arrange the supply line of this section in a vacuum-tight enclosure so that the supply line is not directly exposed to vacuum conditions. The supply line and / or the enclosure must be sufficiently flexible so that the position of the camera relative to the vacuum housing can be adjusted without causing undesired stresses. The vacuum-tight enclosure may form a flexible-walled section within the meaning of the present invention.

[0027] The mask inspection device can be designed so that the adjustment mechanism is not exposed to the vacuum conditions inside the vacuum housing. The adjustment mechanism can include components located outside the vacuum housing. These can specifically be components necessary for operating or controlling the adjustment mechanism. The adjustment mechanism can include components located inside the vacuum housing. These can specifically include components mechanically connected to the EUV camera. The components of the adjustment mechanism located inside the vacuum housing can be surrounded by a flexible wall section. The flexible wall section allows the components to be isolated from the vacuum conditions. The flexible wall section can deform when the position of the EUV camera is adjusted relative to the vacuum housing.

[0028] The present invention does not imply any limitation to a particular structural configuration of the adjustment mechanism, which can be configured, for example, as part of the EUV camera, as part of the vacuum housing, or as a separate structural unit.

[0029] The mask inspection device can have a frame structure arranged in a vacuum housing, the frame structure carrying optical components of the projection lens. The frame structure can be mechanically decoupled from the vacuum housing. As a result, the vacuum housing can deform without mechanical stress being transmitted to the frame structure. The connection between the EUV camera and the frame structure can be through the vacuum housing to which both the frame structure and the EUV camera are attached. In such a design, the EUV camera changes its position relative to the frame structure as a result of disturbing influences. Such influences can be, for example, thermal influences, dynamic influences, pressure differences, or tolerances. The present invention opens up the possibility of compensating for such position changes by adapting the position of the EUV camera relative to the vacuum housing.

[0030] The mask inspection device can include an illumination system that directs EUV radiation emitted from the EUV radiation source onto a photomask disposed within the vacuum housing. The illumination system can be configured to illuminate the photomask with uniform intensity. Optical components of the illumination system can be mounted on a frame structure. In this manner, the projection lens, illumination system, and frame structure can form a mechanical unit. The projection lens of the mask inspection device is typically designed to produce a magnified image of a portion of the photomask on the EUV image sensor. The magnification can be greater than 20, preferably greater than 50, and more preferably greater than 100.

[0031] The EUV camera according to the present invention can have dimensions significantly larger than commercially available photolithography cameras. The camera can weigh, for example, more than 20 kg, preferably more than 50 kg, and more preferably more than 100 kg. The image sensor of the camera can have the shape of a substantially rectangular array. The length of one edge of the rectangle occupied by the array can be, for example, 100 mm to 200 mm. The opening in the vacuum housing through which the EUV camera is attached to the vacuum housing can have a diameter of 500 mm to 1000 mm.

[0032] The photomask inspected in the mask inspection device can have an aspect ratio of, for example, 1:1 to 1:3, preferably 1:1 to 1:2, and particularly preferably 1:1 or 1:2. The photomask can be configured to have a substantially rectangular shape. The photomask preferably has a length and width of 5 to 7 inches (12.7 cm to 17.8 cm), and particularly preferably 6 inches (15.2 cm). In an alternative embodiment, the photomask can have a length of 5 to 7 inches (12.7 cm to 17.8 cm) and a width of 10 to 14 inches (25.4 cm to 35.6 cm), preferably a length of 6 inches (15.2 cm) and a width of 12 inches (30.5 cm).

[0033] The present invention also relates to a method for adjusting a mask inspection device, the mask inspection device including a vacuum housing, an EUV camera, and a projection lens disposed within the vacuum housing for imaging a portion of an EUV photomask onto an image sensor of the EUV camera, the EUV camera being mounted on the vacuum housing, and the position of the EUV camera being adjusted between a first position and a second position relative to the vacuum housing using an adjustment mechanism to adjust the EUV camera relative to an imaging beam path of the projection lens.

[0034] The present disclosure encompasses the development of a method having the features described in the context of a mask inspection device according to the present invention.The present disclosure encompasses the development of a mask inspection device having the features described in the context of a method according to the present invention.

[0035] The invention will now be described by way of example on the basis of advantageous embodiments with reference to the accompanying drawings, in which: FIG. [Brief explanation of the drawings]

[0036] [Figure 1] 1 is a schematic diagram showing a mask inspection apparatus according to the present invention; [Figure 2] FIG. 1 is a schematic diagram showing a photomask. [Figure 3] FIG. 1 is a schematic cross-sectional view showing an EUV camera. [Figure 4] 1 illustrates an embodiment of a mask inspection device according to the present invention; [Figure 5] 10A-10C show alternative embodiments of an adjustment mechanism according to the present invention; [Figure 6] 10A-10C show alternative embodiments of an adjustment mechanism according to the present invention; [Figure 7] FIG. 2 shows a view from the perspective according to FIG. 1 in another embodiment of the present invention. [Figure 8] 8 is a diagram illustrating an embodiment of the mask inspection device of FIG. 7. DETAILED DESCRIPTION OF THE INVENTION

[0037] The mask inspection apparatus shown in FIG. 1 can be used to inspect a microlithography photomask 17.

[0038] Typically, a microlithography photomask 17 is provided for use in a microlithography projection exposure apparatus (not shown). In the microlithography projection exposure apparatus, the photomask 17 is irradiated with extreme ultraviolet radiation (EUV radiation), for example at a wavelength of 13.5 nm, in order to image structures formed on the photomask 17 onto the surface of a lithography object in the form of a wafer. The wafer is coated with a photoresist that is sensitive to EUV radiation. A mask inspection apparatus is used to inspect the photomask for compliance and for contamination.

[0039] According to FIG. 1, a photomask 17 is arranged in a mask inspection apparatus such that an EUV beam path 15 from an EUV radiation source 14 is guided to the photomask 17 via an illumination system 16. The illumination system 16 is used to shape the EUV radiation to form a beam that is used to illuminate an inspection field on the surface of the photomask 17 with uniform brightness. An inspection field 20, which is small compared to the area of ​​the photomask 17, is shown in FIG. 2 in a not-to-scale illustration. For example, the illumination area 20 may have dimensions of 0.5 mm x 0.8 mm. The edge length of the photomask 17 may be, for example, 100 mm to 200 mm. A field stop is arranged in the illumination system 16, which is used to delimit the illumination area into inspection fields 20 on the surface of the photomask 17. To bring different inspection fields 20 into the area of ​​the EUV beam path, the photomask can be moved in a horizontal plane using a positioning mechanism 29.

[0040] The EUV beam path 15 reflected by the photomask 17 continues through a projection lens 22 to an EUV camera 23 equipped with an image sensor 24. The projection lens is used to image the inspection field 20 of the photomask 17 onto the image sensor 24 of the EUV camera 23. The imaging beam path 19 is incident on the image sensor in a Z direction 48. The EUV radiation source 14, illumination system 15, photomask 17, projection lens 22, and image sensor 24 of the EUV camera 23 are disposed within a vacuum chamber 30 surrounded by a vacuum housing 28. During operation of the mask inspection apparatus, a high vacuum exists within the vacuum chamber. The EUV camera 23 includes a camera housing 25 that carries 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 within the vacuum housing 28. The camera housing 25 therefore forms part of the vacuum housing 28 and is subject to the same pressure differential as the other wall regions of the vacuum chamber 30.

[0041] The EUV radiation source 14 is a plasma radiation source in which EUV radiation is emitted from the plasma at a wavelength of 13.5 nm. Tin is a medium that can be used to generate a plasma suitable for emitting such EUV radiation. A laser beam can be formed to strike droplets of the medium to generate the plasma.

[0042] The mirrors in the illumination system 16 and the projection lens 22 are designed as EUV mirrors with a particularly high reflectivity for EUV radiation. The optical region of the EUV mirror 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. Using such a coating, it is possible to reflect approximately 70% of the incident EUV radiation.

[0043] The projection lens 22 has a magnification of more than 100. The area of ​​the image sensor 24 is larger than the area of ​​the inspection field 20 according to the magnification so that the entire generated image of the inspection field 20 of the photomask 17 can be recorded. For example, the image sensor 24 can have dimensions on the order of 100 mm to 200 mm.

[0044] 3, the EUV camera 23 includes a housing 25 on which an image sensor 24 and an electronics unit 27 are disposed. The electronics unit 27 is used to control the image sensor 24, process EUV image data acquired by the image sensor 24, and output it as sensor data. Via supply lines 38, electrical energy is supplied to the EUV camera 23, the sensor data is transferred, and a cooling device (not shown) is operated, which cools the components of the EUV camera 23 to a desired temperature.

[0045] A vacuum flange 31 is formed on the camera housing 25 and extends continuously around the periphery of the camera housing 25. The vacuum flange 31 comprises two circumferential sealing rings 32 arranged one after the other in the direction of the pressure difference that exists across the vacuum flange 31. A connection is established between the EUV camera 23 and the vacuum housing 28 via the vacuum flange 31. When connected, the back surface 26 of the camera housing 25 together with the vacuum housing 28 forms one section of the wall of the vacuum chamber.

[0046] 4, the EUV camera 23 is mounted on the vacuum housing 28 using an adjustment mechanism 33. The EUV camera 23 includes an upper end plate 34 vacuum-tightly connected to a vacuum flange 31 of the EUV camera 23. The adjustment mechanism 33 includes a lower end plate 35 vacuum-tightly connected to the vacuum housing 28. The gap between the upper end plate 34 and the lower end plate 35 is sealed via a flexible wall section in the form of a bellows 37. The bellows 37 extends continuously around the periphery of the EUV camera 23. The vacuum housing 28, the camera housing 25, and the bellows 37 form a section within the wall of the vacuum chamber 30 through which a pressure differential exists between the high vacuum inside the vacuum chamber 30 and the surrounding atmospheric pressure.

[0047] Upper end plate 34 and lower end plate 35 are maintained spaced apart by four actuators 36, with two actuators 36 visible in Figure 4 spaced apart in the X direction and two actuators 36 not visible in Figure 4 spaced apart in the Y direction. The actuators 36 are independently adjustable in length, thereby changing the distance between upper end plate 34 and lower end plate 35 of adjustment mechanism 33. Actuators 36 are positioned radially outward of bellows 37 such that actuators 36 are exposed to atmospheric pressure.

[0048] By appropriate control of the actuators 36, the position of the EUV camera 23 can be adjusted relative to the vacuum housing 28. The EUV camera 23 can be tilted about the Y-axis by lengthening one of the two actuators 36 visible in FIG. 4 and correspondingly shortening the other. The EUV camera 23 can be tilted about the X-axis by lengthening one of the two actuators 36 not visible in FIG. 4 and correspondingly shortening the other. The EUV camera 23 can be displaced in the Z-direction 48 by lengthening or shortening all four actuators 36 together.

[0049] The actuator 36 is controlled by a control unit (not shown in FIG. 4 ). The control unit 39 processes manual input from an operator to generate control commands for the actuator 36. To adjust the mask inspection device for operation, the position of the EUV camera 23 relative to the vacuum housing 28 is adjusted during initial start-up of the device. Further adjustment processes are performed during maintenance operations when the mask inspection device is not in operation. During ongoing operation of the mask inspection device, the actuator 36 is not activated.

[0050] 5 shows another embodiment in which the EUV camera 23 comprises multiple distance sensors 41. The distance sensors 41 are designed to measure the distance to a target 40 mounted on the projection lens 22. Measurements from the distance sensors 41 are processed in a control unit 39 to determine whether the EUV camera 23 has the correct position relative to the projection lens 22. If not, 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 the target 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 apparatus so that the position of the EUV camera 23 is constantly adapted to the current conditions.

[0051] 6, the adjustment mechanism 33 includes a plurality of spacer washers 42 between each of the actuators 36 and the lower end plate 35 of the adjustment mechanism 33. During initial start-up of the mask inspection device, the number of spacer washers 42 is selected individually for each of the actuators 36 to achieve a base setting with approximately the correct alignment of the EUV camera 23 relative to the projection lens 22. Further fine settings are made by the actuators 36 during operation.

[0052] FIG. 7 shows a further embodiment in which the EUV camera 23 is disposed within the vacuum chamber 30 and suspended from the inner surface of the vacuum housing 28. The mask inspection device includes a frame structure 43 that supports the illumination system 16 and the projection lens 22. The frame structure 43 is attached to the vacuum housing 28 via a suspension mechanism 44 that is designed to mechanically decouple the frame structure 43 from the vacuum housing 28. Thus, the vacuum housing 28 can, for example, thermally expand without the thermal expansion being transmitted to the frame structure 43 via the suspension mechanism 44. The photomask 17 is connected to the vacuum housing 28, but not to the frame structure 43. A change in the position of the EUV camera 23 as a result of relative movement between the vacuum housing 28 and the frame structure 43 can be compensated for in accordance with the present invention by changing the position of the EUV camera 23 relative to the vacuum housing 28.

[0053] 8, the vacuum housing 28 includes a housing cover 46 that is vacuum-tightly connected to the vacuum housing 28 via a flange 47. The housing cover 46 carries the EUV camera 23 using a plurality of actuators 36. Because there is no pressure difference between the vacuum condition and the atmosphere across the EUV camera 23, the actuators 36 can be designed for lower actuation forces.

[0054] The actuator 36 extends through the housing cover 46 and is controllable by a control signal via an outer compartment. An inner compartment of the actuator 36 bridges the distance between the housing cover 46 and the EUV camera 23. The inner compartment of the actuator 36 is surrounded by a flexible wall in the form of a tubular membrane 45, so that the inner compartment of the actuator 36 is not exposed to the vacuum conditions inside the vacuum housing 28. A supply line 38 extends through the gap between the housing cover 46 and the EUV camera 23 and is designed to withstand the vacuum conditions.

[0055] The adjustment mechanism includes a plurality of actuators 36, which can displace the EUV camera in the Z direction 48 as described above, and tilt it about the X and Y axes. The adjustment mechanism includes a further actuator 36, the adjustment travel of which is horizontal so that the EUV camera 23 can be displaced in the XY plane relative to the housing cover 46. [Explanation of symbols]

[0056] 14 EUV radiation source 15 EUV beam path 16 Irradiation system 17 Microlithography Mask 19 Imaging beam path 20 inspection fields 22 Projection lens 23 EUV camera 24 image sensors 25 Camera Housing 26 Rear part 28 Vacuum housing 29 Positioning mechanism 30 Vacuum Chamber 31 Vacuum flange 32 Sealing ring 33 Adjustment mechanism 34 Upper end plate 35 Lower end plate 36 Actuator 37 Bellows 38 Supply Line 39 Control Unit 40 Targets 41 Distance Sensor 42 Spacer washer 43 Frame structure 44 Suspension mechanism 45 Tubular membrane 46 Housing cover 47 flange 48 Z direction

Claims

1. 1. A mask inspection device comprising: a vacuum housing (28); an EUV camera (23); and a projection lens (22) disposed inside the vacuum housing (28) for imaging at least a portion (20) of an EUV photomask (17) onto an image sensor (24) of the EUV camera (23), wherein the EUV camera (23) is mounted on the vacuum housing (28), and a position of the EUV camera (23) is adjustable between a first position and a second position relative to the vacuum housing (28) using an adjustment mechanism (33).

2. 2. The mask inspection device of claim 1, wherein the transition of the EUV camera (23) between the first position and the second position comprises a displacement of the EUV camera (23) in a Z direction (48).

3. 3. The mask inspection device of claim 1, wherein the transition of the EUV camera (23) between the first position and the second position includes tilting the EUV camera (23) about an axis perpendicular to the Z direction (48).

4. 4. The mask inspection device of claim 1, wherein the transition of the EUV camera (23) between the first position and the second position comprises a displacement of the EUV camera (23) having a tilt of the EUV camera (23).

5. The mask inspection device of any one of claims 1 to 4, wherein the EUV camera (23) is adjustable between a plurality of positions relative to the vacuum housing (28).

6. The mask inspection device of any one of claims 1 to 5, wherein the adjustment mechanism (33) on the vacuum housing (28) is designed for manual actuation.

7. The mask inspection device according to any one of claims 1 to 6, wherein the adjustment mechanism (33) is designed for actuation by means of an actuator (36).

8. The mask inspection device of any one of claims 1 to 7, wherein the adjustment mechanism (33) has an adjustment travel distance of 0.1 mm to 2 mm.

9. 9. A mask inspection device according to claim 7 or 8, comprising a control unit (39) designed to process input variables to generate control signals for the actuators (36).

10. 10. The mask inspection device of claim 9, wherein the control unit (39) is an element of a closed control loop, the control unit processing measurements on the position of the EUV camera (23) as input variables.

11. The mask inspection device of claim 10, wherein the measurements represent a position of the EUV camera (23) relative to the projection lens (22).

12. 12. The mask inspection device of claim 10 or 11, wherein the measurements represent the position of the EUV camera (23) relative to the vacuum housing (28).

13. The mask inspection device of any one of claims 1 to 12, wherein the vacuum housing (28) includes an opening that is vacuum-tightly closed when the EUV camera (23) is mounted on the vacuum housing (28).

14. 14. The mask inspection device of claim 13, wherein a pressure difference between the interior of the vacuum housing (28) and the ambient exists across the EUV camera (23).

15. The mask inspection device according to any one of the preceding claims, wherein the EUV camera (23) is arranged within the interior of the vacuum housing (28).

16. 16. The mask inspection device of claim 1, wherein a flexible wall section (37, 45) is formed between the EUV camera (23) and the vacuum housing (28), and is subject to deformation when the position of the EUV camera (23) is adjusted relative to the vacuum housing (28).

17. The mask inspection device of any one of claims 1 to 16, wherein the adjustment mechanism (33) is not exposed to vacuum conditions within the interior of the vacuum housing (28).

18. 18. The mask inspection device of claim 1, further comprising a frame structure (43) that carries optical components of the projection lens (22), the frame structure (43) being mechanically decoupled from the vacuum housing (28).

19. 1. A method for adjusting a mask inspection device, the mask inspection device comprising: a vacuum housing (28); an EUV camera (23); and a projection lens (22) disposed inside the vacuum housing (28) for imaging a portion (20) of an EUV photomask (17) onto an image sensor (24) of the EUV camera (23), the EUV camera (23) being mounted on the vacuum housing (28), and a position of the EUV camera (23) being adjusted between a first position and a second position relative to the vacuum housing (28) using an adjustment mechanism (33) to adjust the EUV camera (23) relative to an imaging beam path of the projection lens (22).

Images