Manipulable platform for mounting a camera on a vacuum housing, mask inspection apparatus and method for adjusting a mask inspection apparatus

Abstract

The invention relates to a manipulable platform for mounting a camera on a vacuum housing, to a mask inspection apparatus and to a method for adjusting a mask inspection apparatus. A manipulable platform according to the invention comprises a first assembly (110, 210, 310) which provides a first adjustment mechanism for tilting the platform, the first assembly (110, 210, 310) having a first double-wedge arrangement of two wedge-shaped annular discs (111, 112, 211, 212, 311, 312) which are rotatably mounted one on the other about a predefined axis via a first ball bearing (115, 215, 315).

Description

[0001]

[0002] Manipulable platform for mounting a camera on a vacuum housing, mask inspection apparatus and method for adjusting a mask inspection apparatus

[0003] The present application claims the priority of the German patent application DE 10 2024 123 006.1 , filed on August 12, 2024. The content of this DE application is incorporated by reference in the present application text.

[0004] BACKGROUND OF THE INVENTION

[0005] Field of the invention

[0006] The invention relates to a manipulable platform for mounting a camera on a vacuum housing, to a mask inspection apparatus and to a method for adjusting a mask inspection apparatus.

[0007] Prior art

[0008] Microlithography is used for producing microstructured components, such as integrated circuits or LCDs. The microlithography process is performed in what is known as a projection exposure apparatus, which comprises an illumination device and a projection lens. The image of a mask (= reticle) illuminated by means of the illumination device is in this case projected by means of the projection lens onto a substrate (e.g. a silicon wafer) coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection lens, in order to transfer the mask structure to the light-sensitive coating on the substrate.

[0009] In order to check that the mask has sufficient imaging capability before being used in the lithography process, it is known practice to use mask inspection apparatuses which comprise, within a vacuum housing, an illumination system and a projection lens, with the projection lens imaging the illuminated region of the mask onto an image sensor of an (EUV) camera. In this case, the mask inspection apparatus should be adjusted in such a way that the mask is satisfactorily imaged onto the image sensor. A possible approach for this involves the implementation of an EUV camera, the position of which relative to the imaging beam path of the projection lens or to a vacuum housing containing the latter is discretely or continuously adjustable.

[0010] However, in practice, implementing such an adjustability of a mask inspection apparatus or a corresponding actuation of the camera is a demanding challenge in many respects. A circumstance which makes it more difficult to provide the corresponding manipulability is in particular that the pressure differences present between the inside of the vacuum chamber (at a vacuum of e.g. the order of magnitude of 10’5mbarjand the surrounding area (at atmospheric pressure, of approximately 1 bar) mean that it is necessary, depending on the size, i.e. diameter, of the camera, to transfer very high loads, and at the same time it is necessary to take account of requirements concerning long-term stability, vacuum tightness, and structural space restrictions that typically exist. Furthermore, there is also a need for the correspondingly actuated camera, which is in its respective desired position, to be held stably in that position without the positional stability being associated with an undesirably high input of energy into the system.

[0011] SUMMARY OF THE INVENTION

[0012] Against the above background, an object of the present invention is to provide a manipulable platform for mounting a camera on a vacuum housing, a mask inspection apparatus and a method for adjusting a mask inspection apparatus which enable an adjustment while at least partly avoiding the problems described above.

[0013] This object is achieved according to the features of the independent claims.

[0014] According to one aspect, the invention relates to a manipulable platform for mounting a camera on a vacuum housing, comprising a first assembly which provides a first adjustment mechanism for tilting the platform, the first assembly having a first double-wedge arrangement of two wedge-shaped annular discs which are rotatably mounted one on the other about a predefined axis via a first ball bearing.

[0015] According to one embodiment, the two wedge-shaped annular discs have matching wedge angles.

[0016] According to one embodiment, the first adjustment mechanism allows the platform to tilt about two axes orthogonal to one another and to the predefined axis.

[0017] The predefined axis may in particular be a central axis. The central axis may have a direction perpendicular to a surface of an image sensor of the camera (in particular EUV camera), in particular to a surface of the image sensor for detecting light (in particular EUV light). The central axis of the camera may preferably be perpendicular to all the surfaces of the camera that are designed to detect light, i.e. EUV light. The central axis may, for example, intersect a centre of gravity of the camera, it being possible for the camera to have any desired geometry, for example cylindrical or cuboid.

[0018] The invention is in particular based on the concept of providing a manipulable platform, intended for mounting a camera on a vacuum housing, with at least one first assembly in which two wedge-shaped annular discs (which can in particular have matching wedge angles) are combined and rotatably mounted via a ball bearing in such a way that - as described in more detail below - rotating either just one of the two wedge-shaped annular discs or both wedge-shaped annular discs makes it possible to set different tilt angles (corresponding to the degrees of freedom Rxand Ry) for the manipulate platform and a camera mounted thereon.

[0019] Specifically, as described in more detail below, in this way it is possible to set any desired solid angle ranging between zero and twice the wedge angle of the respective wedge-shaped annular discs. At the same time, the wedge-shaped annular discs are centred via the ball bearing.

[0020] One advantage of the arrangement according to the invention is in particular that considerable force absorption, i.e. load transfer, already occurs via the ball bearing. In the application scenario targeted in particular according to the invention, that of an adjustable mask inspection apparatus with a correspondingly actuatable camera, the result of this is that negative effects of providing the necessary adjustment mechanism on the long-term stability and the vacuum tightness can be avoided or at least minimized.

[0021] Overall, the present invention provides a manipulable platform which is capable of bearing relatively high loads but also is able to be operated, i.e. driven, with relatively low forces. Another advantage is that a positional and pose stability of the platform and of a camera mounted thereon can be realized with a relatively low expenditure of force and thus without significant input of energy into the system, specifically substantially in self-locking fashion.

[0022] According to one embodiment, at least one of the wedge-shaped annular discs is assigned a tangential drive for rotating the respective annular disc about the predefined axis.

[0023] In further embodiments of the invention, the manipulable platform according to the invention also provides, in addition or as an alternative to the above-described adjustability in the degrees of freedom Rxand Ry(i.e. tilting about the x- or y-axis orthogonal to the predefined axis) a manipulability corresponding to the translational degree of freedom in the movement along said predefined axis (i.e. in the z-direction). For this, in embodiments the manipulable platform according to the invention has a second assembly, it being possible for the first and the second assembly in turn to be mounted one on the other via a ball bearing.

[0024] According to one embodiment, this second assembly has a second doublewedge arrangement of two wedge elements which have matching wedge angles and are mounted one on the other via a ball bearing. It is possible in particular for one of these wedge elements to be movably mounted along an axis perpendicular to the predefined axis via a linear bearing, this movement being associated with a translational movement of the respective other wedge element along the predefined axis. For this, the other wedge element in question may be fixed in place, i.e. prevented from correspondingly moving, along said axis (in which the translational movement of the first wedge element takes place) perpendicular to the predefined axis by corresponding stops, with the result that said second wedge element can be displaced only along the predefined axis to achieve the desired z-adjustability.

[0025] According to one embodiment, the first wedge element is assigned a linear drive for moving this first wedge element along an axis perpendicular to the predefined axis.

[0026] In a further embodiment, the second assembly may also have an arrangement of two annular-disc elements, of which the mutually facing surfaces form a double-helix geometry and which are mounted one on the other via a ball bearing with a helical ball guide. This configuration in particular has the advantage that less structural space in the lateral direction (i.e. the direction perpendicular to the predefined axis) is needed than for the above-described embodiment (with a wedge element translationally movably mounted transversely to the predefined axis).

[0027] According to one embodiment, one of the annular-disc elements is assigned a tangential drive for rotating the respective annular-disc element about the predefined axis.

[0028] According to one embodiment, the camera is an EUV camera.

[0029] The invention further also relates to a mask inspection apparatus comprising a vacuum housing, an EUV camera and a projection lens, which is located in a vacuum chamber of the vacuum housing, for imaging at least one portion of an EUV mask onto an image sensor of the EUV camera, wherein the EUV camera is mounted on the vacuum housing via a manipulable platform having the features described above.

[0030] The invention further also relates to a method for adjusting a mask inspection apparatus, wherein the mask inspection apparatus comprises a vacuum housing, an EUV camera and a projection lens, which is located in a vacuum chamber of the vacuum housing, for imaging at least one portion of an EUV mask onto an image sensor of the EUV camera, wherein the EUV camera is mounted on the vacuum housing via a manipulable platform having the features described above, and wherein the position of the EUV camera is adjusted relative to the vacuum housing, in order to adjust the EUV camera relative to the imaging beam path of the projection lens.

[0031] Further configurations of the invention can be gathered from the description and the dependent claims.

[0032] The invention is explained in more detail below on the basis of preferred exemplary embodiments and with reference to the attached figures.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In the figures:

[0035] Figure 1 shows a schematic illustration for elucidating the structure of a manipulable platform for mounting a camera on a vacuum housing, according to a first embodiment of the invention;

[0036] Figure 2 shows a schematic illustration for elucidating the structure of a manipulable platform for mounting a camera on a vacuum housing, according to a second embodiment of the invention;

[0037] Figure 3 shows a schematic illustration for elucidating the structure of a manipulable platform for mounting a camera on a vacuum housing, according to a third embodiment of the invention; and

[0038] Figure 4 shows a schematic illustration for elucidating a possible basic structure of a mask inspection apparatus.

[0039] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0040] Different exemplary embodiments of a manipulable platform according to the invention are described below with reference to the schematic illustrations in Figures 1 to 3.

[0041] A common feature of these embodiments is that a respective at least one (first) assembly 110, 210 and 310 with two wedge-shaped annular discs rotatably mounted one on the other via a ball bearing is provided, in order to enable an adjustability of the manipulable platform (and of a camera mounted thereon) by different tilt angles corresponding to the degrees of freedom Rxand Ry. In this case, the embodiments in Figure 2 and Figure 3 that are yet to be described in detail below also include, in addition to this tiltability, an adjustability corresponding to the translational degree of freedom of movement in the z-direction, with a (second) assembly 220 and 320 in Figure 2 and Figure 3, respectively, which is provided for this purpose being implemented in different ways.

[0042] With reference initially to Figure 1 , said first assembly is denoted "110", the two said wedge-shaped annular discs being denoted "111 " and "112". Said ball bearing is denoted "115". The manipulate platform is denoted "100" and has a base 130 which can be mounted on a vacuum housing (not illustrated in Figure 1 ), and a through-opening for a camera 150, which is indicated in Figure 1. The camera 150 has a camera flange 151 via which it is fixed to a further (not wedge- shaped) annular disc 113. The annular disc 113 is mounted on the wedge- shaped annular disc 112 via a further ball bearing 116, and the first wedge- shaped annular disc 111 is rotatably mounted on the base 130 via a ball bearing 114. "140" denotes a central axis about which the arrangement according to Figure 1 may be rotationally symmetrical in respect of some of its components. Although reference is made here and in the further embodiments described to a "central axis", it may also generally speaking be a predefined axis.

[0043] As Figure 1 also indicates, the first wedge-shaped annular disc 111 can be driven via a tangential drive 105 and rotated about the central axis 140, and the second wedge-shaped annular disc 112 can be driven via a further tangential drive 106 and rotated about the central axis 140. "125" denotes a vacuum seal component which may in particular have a folded structure (in the form of a "bellows").

[0044] In an advantageous application scenario of the invention, the camera 150 may be an EUV camera of a mask inspection apparatus (as described in more detail with reference to Figure 4), the manipulable platform 100, 200 and 300 according to the invention in that case allowing an adjustment of this mask inspection apparatus by way of an adjustability of the camera relative to a vacuum housing of the mask inspection apparatus in said degrees of freedom. The manipulable platform 100, 200 and 300 then forms a mounting interface between the camera and the vacuum housing, the vacuum housing then containing in particular a projection lens for imaging an EUV mask onto an image sensor of the camera, as described in more detail below.

[0045] With reference to Figure 1 again, rotating either just one of the two wedge- shaped annular discs 111 , 112 or both wedge-shaped annular discs 111 and 112 about the central axis 140 makes it possible to set any desired solid angle ranging between zero and twice the wedge angle of the respective wedge- shaped annular discs 111 , 112 for the manipulable platform 100 according to the invention and the camera 150 mounted thereon, the wedge-shaped annular discs 111 , 112 each being centred via the ball bearing 115. The effect of this is to tilt the manipulable platform 100 and the camera 150 by twice the wedge angle when the two wedge-shaped annular discs 111 , 112 have matching wedge directions (i.e. the relative rotational angle is 0°). A rotation of both annular discs 111 , 112 in the same direction in this position makes it possible to rotate the resulting wedge in space. A rotational angle of 180° between the two wedge- shaped annular discs 111 , 112 corresponds, owing to the plane-parallel geometry thus formed overall of the double-wedge arrangement, to a tilt angle of 0° for the platform 100 and the camera 150, whereas when only one of the two annular discs 111 or 1 12 is rotating, different tilt angles up to the aforementioned maximum tilt angle can be implemented.

[0046] Advantageous wedge angles are between >0° and 10°. If the wedge angles are not exactly the same, there is a resulting wedge angle between the difference and the sum of the wedge angles. If they are exactly the same, the minimum resulting wedge angle is 0°.

[0047] Owing to the combination of the double-wedge arrangement of the wedge- shaped annular discs 111 , 112 with the ball bearing 115, the above-described manipulability of the platform 100 and of the camera 150 mounted thereon in the degrees of freedom Rxand Ryis particularly advantageously realized, insofar as the ball bearing 115 allows not only a centring of the annular discs 111 and 112 but also a significant force absorption, i.e. load transfer, with the result that even in the event of the high loads that occur owing to the existing pressure differences in the application scenario described in the introduction, that of a mask inspection apparatus, the requirements of long-term stability and vacuum tightness can be met.

[0048] In addition, it is possible with a relatively small expenditure of force and without a significant input of energy into the system to ensure the respective positional and pose stability of the platform 100 and of the camera 150 in self-locking fashion, for which it is enough merely to brake the tangential drives 105, 106 (and therefore complex pose regulation, for instance, is not necessary).

[0049] Described below with reference to Figure 2 and Figure 3 are embodiments in which, in addition to the manipulation in the degrees of freedom Rxand Rythat is achieved according to Figure 1 , a manipulability in the translational degree of freedom of the movement along the z-axis is enabled. In this respect, in Figure 2 and Figure 3, components that are the same or have substantially the same function as those in Figure 1 are each denoted by reference numerals increased by "100" (in Figure 2) and "200" (in Figure 3).

[0050] With reference initially to Figure 2, a manipulable platform comprises two annular-disc elements 221 , 222 for said manipulability in the z-direction, i.e. along the central axis 240, the first of these annular-disc elements 221 being assigned a tangential drive 207 for rotation about the central axis 240. The two annular-disc elements 221 , 222 have a double-helix geometry on the mutually facing surfaces and are mounted one on the other via a ball bearing 217 formed with a helical ball guide. This can be seen best in Figure 2 at the position of the ball guide of the ball bearing 217 that is shown on the right in the illustration in comparison with the position of this ball guide that is shown on the left in the illustration. This configuration has the effect that a rotation of the annular-disc element 221 about the central axis 240 brought about via the tangential drive 207 causes a change in the overall thickness of the arrangement of the two annular-disc elements 221 , 222 and thus the desired translational movement of the camera 250 along the z- axis.

[0051] The advantage of the embodiment according to Figure 2 - in addition to the selfcentring and direct force transfer achieved in turn via the ball bearing that is present - is a particularly compact design and thus a saving on structural space, for instance in comparison with the embodiment described below with reference to Figure 3 (which is comparatively easier to manufacture). According to Figure 3, by contrast to Figure 2, the second assembly 320, which is present to provide the manipulability in the translational degree of freedom of the mobility in the z-direction, comprises two wedge elements 321 , 322, which according to Figure 3 (and also by contrast to Figure 2) are located below the first assembly, i.e. on the first-assembly side facing away from the camera flange 351 and towards the base 330. Of these two wedge elements 321 , 322, the first wedge element 321 is movably mounted along an axis (x-axis) perpendicular to the central axis 340, as indicated via the horizontal double-headed arrow, via a linear drive 307, with a corresponding ball bearing between the first wedge element 321 and the base 330 and between the first wedge element 321 and the second wedge element 322 being denoted "319" and "318", respectively. "314" denotes a ball bearing between the second assembly 320, i.e. its second wedge element 322, and the first assembly 310, i.e. its first wedge-shaped annular disc 311 . As indicated in Figure 3, the first wedge element 321 of the second assembly has a slot for allowing said movement of the first wedge element 321 in a direction perpendicular to the central axis 340.

[0052] The second wedge element 322 of the second assembly is, by contrast to the first wedge element 321 , stationary in a horizontal direction (which is to say a direction in the lateral plane) that is perpendicular to the z-axis, i.e. central axis 340, and prevented from a corresponding sideways movement, as indicated symbolically in Figure 3 on the right by a stop 335. As a result, during the abovedescribed movement of the first wedge element 321 along an axis (x-axis) perpendicular to the central axis 340, said second wedge element 322 can be displaced only in a direction along the z-axis, the effect of which is the desired translational z-movement of the camera 350.

[0053] Figure 4 shows a schematic illustration for elucidating a possible basic structure of a mask inspection apparatus. Accordingly, a mask inspection apparatus in particular comprises an illumination system 450 and a projection lens 460, wherein an EUV beam path 445 originating from an EUV radiation source 440 is routed via the illumination system 450 onto an EUV mask 470. The illumination system 450 is used to shape the EUV radiation to form a beam used to illuminate, with uniform brightness, an examination field on the surface of the EUV mask 470. The illuminated region of the mask 470 may, for example, have dimensions of 0.5 mm * 0.8 mm. The edge lengths of the EUV mask 470 may, for example, be between 100 mm and 200 mm. A field stop used to delimit the illuminated region to the examination field on the surface of the EUV mask 470 is arranged in the illumination system 450. Using a positioning mechanism 471 , it is possible to move the EUV mask 470 in the horizontal plane in order to bring different examination fields into the region of the EUV beam path. The EUV mask 470 may, for example, have an aspect ratio of between 1 :1 and 1 :3, preferably between 1 :1 and 1 :2, particularly preferably of 1 :1 or 1 :2; it can be of substantially rectangular design.

[0054] The EUV beam path 445 reflected at the EUV mask 470 continues through the projection lens 460 to an EUV camera 410, which is equipped with an image sensor 411 . The projection lens 460 is used to image the examination field of the EUV mask 470 onto the image sensor 411 of the EUV camera 410. The imaging beam path 445 is incident on the image sensor 411 in the z-direction. The EUV radiation source 440, the illumination system 450, the EUV mask 470, the projection lens 460 and the image sensor 411 of the EUV camera 410 are arranged in a vacuum chamber 430 surrounded by a vacuum housing 406. During operation of the mask inspection apparatus, a high vacuum is present in the vacuum chamber 430. The EUV camera 410 comprises a camera housing 412, which carries the image sensor 411. A back part 413 of the camera housing 412 projects out of the vacuum housing 406, while the image sensor 411 is exposed to the vacuum in the vacuum housing 406.

[0055] The EUV radiation source 440 is a plasma radiation source for generating EUV radiation at a wavelength of approximately 13.5 nm.

[0056] The mirrors in the illumination system 450 and the mirrors in the projection lens 460 are designed as EUV mirrors which have a particularly high reflectivity for EUV radiation. The optical surface of the EUV mirrors may be formed by a highly reflective coating. This can be a multilayer coating, in particular a multilayer coating having alternating layers of molybdenum and silicon. Using such a coating, it is possible to reflect approximately 70% of the incident EUV radiation. The projection lens 460 has a magnification factor of more than 100. In order to be able to record the entirety of the generated image of the examination field of the EUV mask 470, the area of the image sensor 411 is greater than the area of the examination field in accordance with the magnification factor. The image sensor 411 can have dimensions of the order of magnitude of 100 mm to 200 mm, for example.

[0057] Even though the invention has been described on the basis of specific embodi- ments, numerous variations and alternative embodiments will be apparent to a person skilled in the art, for example by combining and / or exchanging features of individual embodiments. Accordingly, it goes without saying for a person skilled in the art that such variations and alternative embodiments are also included by the present invention, and the scope of the invention is restricted only within the meaning of the accompanying claims and the equivalents thereof.

Claims

Claims1. Manipulable platform for mounting a camera (150, 250, 350) on a vacuum housing, comprising• a first assembly (110, 210, 310) which provides a first adjustment mechanism for tilting the platform, the first assembly (110, 210, 310) having a first double-wedge arrangement of two wedge-shaped annular discs (111 , 112, 211 , 212, 311 , 312) which are rotatably mounted one on the other about a predefined axis via a first ball bearing (115, 215, 315).

2. Manipulable platform according to Claim 1 , characterized in that the two wedge-shaped annular discs (111 , 112, 211 , 212, 311 , 312) have matching wedge angles.

3. Manipulable platform according to Claim 1 or 2, characterized in that the first adjustment mechanism allows the platform to tilt about two axes orthogonal to one another and to the predefined axis.

4. Manipulable platform according to one of Claims 1 to 3, characterized in that the predefined axis is a central axis (140, 240, 340).

5. Manipulable platform according to one of the preceding claims, characterized in that at least one of the wedge-shaped annular discs (111 , 112, 211 , 212, 311 , 312) is assigned a tangential drive (105, 106, 205, 206, 305, 306) for rotating the respective annular disc about the predefined axis.

6. Manipulable platform according to one of the preceding claims, characterized in that it comprises a second assembly (220, 320) which provides a second adjustment mechanism for translationally moving the platform along the predefined axis.

7. Manipulable platform according to Claim 6, characterized in that this second assembly (320) has a second double-wedge arrangement of two wedge elements (321 , 322) which have matching wedge angles and are mounted one on the other via a second ball bearing (318).

8. Manipulable platform according to Claim 7, characterized in that a first wedge element (321 ) of these wedge elements is movably mounted along an axis perpendicular to the predefined axis via a linear bearing (319), this movement being associated with a translational movement of the second wedge element (322) of these wedge elements along the predefined axis.

9. Manipulable platform according to Claim 8, characterized in that the first wedge element (321 ) is assigned a linear drive (307) for moving this first wedge element (321 ) along an axis perpendicular to the predefined axis.

10. Manipulable platform according to Claim 6, characterized in that the second assembly (220) has an arrangement of two annular-disc elements (221 , 222), of which the mutually facing surfaces form a double-helix geometry and which are mounted one on the other via a ball bearing (216) with a helical ball guide.11 . Manipulable platform according to Claim 10, characterized in that one of the annular-disc elements (221 ) is assigned a tangential drive (207) for rotating the respective annular-disc element (221 ) about the predefined axis.

12. Manipulable platform according to one of the preceding claims, characterized in that the camera (150, 250, 350) is an EUV camera.

13. Mask inspection apparatus comprising a vacuum housing (406), an EUV camera (410) and a projection lens (460), which is located in a vacuum chamber (430) of the vacuum housing (406), for imaging at least one portion of an EUV mask (470) onto an image sensor (411 ) of the EUV camera (410), characterized in that the EUV camera (410) is mounted on the vacuumhousing (406) via a manipulable platform according to one of Claims 1 to 12.

14. Method for adjusting a mask inspection apparatus, wherein the mask inspection apparatus comprises a vacuum housing (406), an EUV camera(410) and a projection lens (460), which is located in a vacuum chamber (430) of the vacuum housing (406), for imaging at least one portion of an EUV mask (470) onto an image sensor (411 ) of the EUV camera (410), wherein the EUV camera (410) is mounted on the vacuum housing (406) via a manipulable platform according to one of Claims 1 to 12; and wherein the position of the EUV camera (410) is adjusted relative to the vacuum housing (406), in order to adjust the EUV camera (410) relative to the imaging beam path of the projection lens (460).

Images