Manipulable platform for mounting a camera on a vacuum housing, as well as mask inspection device and method for adjusting a mask inspection device

Abstract

The invention relates to a manipulable platform for mounting a camera on a vacuum housing, as well as to a mask inspection device and a method for adjusting a mask inspection device. 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) comprises a first double wedge arrangement consisting of two wedge-shaped annular disks (111, 112, 211, 212, 311, 312) which are mounted on one another via a first ball bearing (115, 215, 315) for rotation about a predetermined axis.

Description

BACKGROUND OF THE INVENTIONField of the invention

[0001] The invention relates to a manipulable platform for mounting a camera on a vacuum housing, as well as a mask inspection device and a method for adjusting a mask inspection device. State of the art

[0002] Microlithography is used to manufacture microstructured components, such as integrated circuits or LCDs. The microlithography process is carried out in a so-called projection exposure system, which has an illumination device and a projection lens. The image of a mask (= reticle) illuminated by the illumination device is projected by 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 of the substrate.

[0003] To test the mask for sufficient imaging capability before use in the lithography process, the use of mask inspection devices is known. These devices comprise an illumination system and a projection lens within a vacuum housing. The illuminated area of ​​the mask is imaged onto an image sensor of an (EUV) camera using the projection lens. The mask inspection device must be adjusted in such a way that a perfect image of the mask is obtained on the image sensor. One possible approach involves implementing an EUV camera whose position can be discretely or continuously adjusted relative to the imaging beam path of the projection lens or to a vacuum housing that accommodates it.

[0004] However, the realization of such adjustability of a mask inspection device or a corresponding actuation of the camera represents a demanding challenge in practice in several respects. One circumstance that complicates the provision of the corresponding manipulation is, in particular, the existing pressure differences between the interior of the vacuum chamber (with a vacuum of, for example, on the order of 10 -5mbar) and the environment (atmospheric pressure of approximately 1 bar) mean that, depending on the size or diameter of the camera, very high loads must be absorbed. At the same time, requirements for long-term stability, vacuum tightness, and typically existing installation space limitations must be taken into account. Furthermore, there is also a need to keep the appropriately actuated camera in its desired position stable in its position without the positional stability being accompanied by an undesirably high energy input into the system.

[0005] US 2022 / 0171332 A1 discloses, among other things, an imaging system in which a sealed housing with a camera located therein is arranged within a hermetic chamber or vacuum chamber, wherein the housing can be arranged on linear sliding tables and is mounted displaceably along at least one axis.

[0006] DE 10 2022 202 938 A1 discloses, among other things, in a projection exposure system, an arrangement with a first component which is connected to a second component via an adjustable interface, and with a spacer which has a plate-shaped or a wedge-shaped geometry and is designed to adjust the second component in one translational degree of freedom and in two rotational degrees of freedom relative to the first component.

[0007] DE 10 2008 026 979 B3 discloses a device for correcting image aberrations in an optical system, having an optical element held by an inner mount, wherein the inner mount is connected to an outer mount and wherein a rotary wedge gear or a sliding wedge gear is provided for adjusting the position of the inner mount relative to the outer mount.

[0008] DE 10 2014 222 271 A1 discloses a mask inspection system for inspecting a lithography mask, comprising a placement table that can be moved in two independent directions for placing a lithography mask, wherein the placement table divides a space into two half-spaces within a plane defined by it, and wherein the lithography mask is located in one half-space. SUMMARY OF THE INVENTION

[0009] Against the above background, it is an object of the present invention to provide a manipulable platform for mounting a camera on a vacuum housing, as well as a mask inspection device and a method for adjusting a mask inspection device, which enable adjustment while at least partially avoiding the problems described above.

[0010] This problem is solved according to the features of the independent patent claims.

[0011] 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, wherein the first assembly has a first double wedge arrangement of two wedge-shaped annular discs which are rotatably mounted on one another about a predetermined axis via a first ball bearing.

[0012] According to one embodiment, the two wedge-shaped annular discs coincide in their wedge angle.

[0013] According to one embodiment, the first adjustment mechanism enables tilting of the platform about two axes orthogonal to each other and to the predetermined axis.

[0014] The predetermined axis can, in particular, be a central axis. The central axis can have a direction perpendicular to a surface of an image sensor of the camera (in particular an EUV camera), in particular to a surface of the image sensor for capturing light (in particular EUV light). The central axis of the camera can preferably be perpendicular to all surfaces of the camera designed for capturing light or EUV light. The central axis can, for example, intersect a center of gravity of the camera, whereby the camera can have any geometry, for example, cylindrical or cuboid.

[0015] The invention is based in particular on the concept of providing a manipulable platform for mounting a camera on a vacuum housing, comprising at least one first assembly in which two wedge-shaped annular discs (which may coincide in particular with regard to their wedge angle) are combined and rotatably mounted via a ball bearing in such a way that - as will be described in more detail below - by rotating either only one of the two wedge-shaped annular discs or both wedge-shaped annular discs, different tilt angles (corresponding to the degrees of freedom R x and R y ) can be adjusted.

[0016] Specifically, as described in more detail below, any solid angle can be set in this way, ranging from zero to twice the wedge angle of the respective wedge-shaped ring discs. The ball bearing also simultaneously centers the wedge-shaped ring discs.

[0017] A particular advantage of the arrangement according to the invention is that the ball bearing already absorbs a considerable amount of force or load. In the application scenario specifically envisaged by the invention, an adjustable mask inspection device with a correspondingly actuatable camera, this means that the negative effects of providing the required adjustment mechanism on long-term stability and vacuum tightness can be avoided or at least minimized.

[0018] Overall, the present invention provides a manipulable platform that is capable of bearing comparatively high forces, yet can be operated or driven with comparatively low forces. A further advantage is that the positional and orientation stability of the platform or a camera mounted on it can be achieved with comparatively little force and thus without significant energy input into the system, namely, essentially self-locking.

[0019] According to one embodiment, at least one of the wedge-shaped ring discs is assigned a tangential drive for rotating the respective ring disc about the predetermined axis.

[0020] In further embodiments of the invention, the manipulable platform according to the invention, in addition to or alternatively to the adjustability in the degrees of freedom R described above,x and R y (i.e., tilting about the x- or y-axis orthogonal to the given axis) also provides manipulability corresponding to the translational degree of freedom of the displacement along said given axis (i.e., in the z-direction). For this purpose, the manipulable platform according to the invention has, in embodiments, a second assembly, wherein the first and second assemblies can in turn be mounted on one another via a ball bearing.

[0021] According to one embodiment, this second assembly has a second double wedge arrangement consisting of two wedge elements which match in their wedge angle and are mounted on one another via a ball bearing. In particular, one of these wedge elements can be mounted displaceably via a linear bearing along an axis perpendicular to the predetermined axis, wherein this displacement is accompanied by a translational displacement of the other wedge element along the predetermined axis. For this purpose, the other wedge element in question can be fixed along the said axis perpendicular to the predetermined axis (in which the translational displacement of the first wedge element occurs) by appropriate stops or can be prevented from corresponding displacement, with the result that said second wedge element can only deflect along the predetermined axis to achieve the desired z-adjustability.

[0022] According to one embodiment, the first wedge element is assigned a linear drive for displacing this first wedge element along an axis perpendicular to the predetermined axis.

[0023] In a further embodiment, the second assembly can also comprise an arrangement of two annular disc elements whose mutually facing surfaces form a double-helix geometry and are mounted on one another via a ball bearing with a helical ball guide. This configuration has the particular advantage that, compared to the previously described embodiment (with a wedge element mounted for translational displacement transversely to the specified axis), less installation space is required in the lateral direction (i.e., perpendicular to the specified axis).

[0024] According to one embodiment, a tangential drive for rotating the respective ring disc element about the predetermined axis is assigned to one of the ring disc elements.

[0025] According to one embodiment, the camera is an EUV camera.

[0026] The invention further relates to a mask inspection device, comprising a vacuum housing, an EUV camera and a projection lens arranged in a vacuum chamber of the vacuum housing for imaging at least a section 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.

[0027] The invention further relates to a method for adjusting a mask inspection device, wherein the mask inspection device has a vacuum housing, an EUV camera and a projection lens arranged in a vacuum chamber of the vacuum housing for imaging at least a section 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 with 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.

[0028] Further embodiments of the invention can be found in the description and the dependent claims.

[0029] The invention is explained in more detail below using preferred embodiments with reference to the attached figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] They show: Fig. 1 is a schematic diagram illustrating the structure of a manipulable platform for mounting a camera on a vacuum housing according to a first embodiment of the invention; Fig. 2 is a schematic diagram illustrating the structure of a manipulable platform for mounting a camera on a vacuum housing according to a second embodiment of the invention; Fig. 3 is a schematic diagram illustrating the structure of a manipulable platform for mounting a camera on a vacuum housing according to a third embodiment of the invention; and Fig. 4 a schematic representation to explain a possible basic structure of a mask inspection device. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0031] In the following, different exemplary embodiments of a manipulable platform according to the invention are described with reference to the schematic representations of Fig. 1 to Fig. 3 described.

[0032] These embodiments have in common that at least one (first) assembly 110, 210 or 310 is provided with two wedge-shaped annular discs, which are rotatably mounted on one another via a ball bearing, in order to enable the manipulable platform (or a camera mounted thereon) to be adjusted by different tilt angles according to the degrees of freedom R x and R y The embodiments of the invention described in more detail below include Fig. 2 and Fig. 3 in addition to this tiltability also an adjustability according to the translational degree of freedom of the displacement in the z-direction, whereby for this purpose provided (second) assembly 220 or 320 in Fig. 2 and Fig. 3 is realized in different ways.

[0033] With reference first to Fig. 1, the said first assembly is designated by "110", with the two said wedge-shaped annular discs being designated by "111" and "112" respectively. The said ball bearing is indicated by "115". The manipulable platform is designated by "100" and has a Fig. 1 not shown) mountable base 130 and a passage opening for a Fig. 1. The camera 150 has a camera flange 151, via which it is fixed to a further (non-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 Fig. 1 may be rotationally symmetrical with respect to some of its components. Although reference is made here and in the further described embodiments to a "central axis," this may also generally be a predetermined axis.

[0034] As also in Fig. As indicated in Figure 1, the first wedge-shaped annular disc 111 is drivable via a tangential drive 105 and rotatable about the central axis 140, and the second wedge-shaped annular disc 112 is drivable via a further tangential drive 106 and rotatable about the central axis 140. "125" denotes a vacuum sealing component, which may in particular have a pleated structure (as a "bellows").

[0035] In an advantageous application scenario of the invention, the camera 150 may be an EUV camera of a mask inspection device (as described with reference to Fig. 4 below), wherein the manipulable platform 100, 200, or 300 according to the invention then enables adjustment of this mask inspection device by adjusting the camera relative to a vacuum housing of the mask inspection device in the aforementioned degrees of freedom. The manipulable platform 100, 200, or 300 then forms a mounting interface between the camera and the vacuum housing, wherein, as described below, a projection lens for imaging an EUV mask onto an image sensor of the camera is arranged in the vacuum housing.

[0036] With further reference to Fig. 1, by rotating either only one of the two wedge-shaped ring disks 111, 112 or both wedge-shaped ring disks 111 and 112 around the central axis 140, any solid angle in the range between zero and twice the wedge angle of the respective wedge-shaped ring disks 111, 112 can be set for the manipulable platform 100 according to the invention or the camera 150 mounted thereon, wherein the wedge-shaped ring disks 111, 112 are centered via the ball bearing 115. In this case, a tilt of the manipulable platform 100 or the camera 150 by twice the wedge angle is achieved if both wedge-shaped ring disks 111, 112 coincide with respect to the wedge direction (i.e., the relative angle of rotation is 0°). A rotation of both ring discs 111, 112 in this position in the same direction enables a rotation of the resulting wedge in space.A rotation angle of 180° between the two wedge-shaped ring disks 111, 112 corresponds to a tilt angle of 0° for the platform 100 or the camera 150 due to the overall plane-parallel geometry of the double wedge arrangement thus formed, whereas when only one of the two ring disks 111 or 112 is rotated, different tilt angles up to the above-mentioned maximum tilt angle can be realized.

[0037] Advantageous wedge angles are between >0° and 10°. If the wedge angles are not exactly equal, the resulting wedge angle is the difference between the two wedge angles and the sum of the two. If they are exactly equal, the minimum resulting wedge angle is 0°.

[0038] The manipulability of the platform 100 or the camera 150 mounted thereon in the degrees of freedom R x and R yis realized in a particularly advantageous manner as a result of the combination of the double wedge arrangement of the wedge-shaped ring disks 111, 112 with the ball bearing 115 in that the ball bearing 115 not only enables centering of the ring disks 111 and 112 but also enables significant force absorption or load transfer, with the result that the requirements of long-term stability and vacuum tightness can be met even in the application scenario of a mask inspection device described in the introduction due to the existing pressure differences, which occur due to the high loads.

[0039] In addition, the respective position and attitude stability of the platform 100 or the camera 150 can be ensured in a self-locking manner with comparatively little effort and without significant energy input into the system, for which only braking of the tangential drives 105, 106 is sufficient (so that, for example, complex attitude control is unnecessary).

[0040] In the following, with reference to Fig. 2 and Fig. 3 embodiments are described in which, in addition to the Fig. 1 achieved manipulation in the degrees of freedom R x and R y a manipulation in the translational degree of freedom of the displacement along the z-axis is possible. Fig. 2 and Fig. 3 each compared to Fig. 1 analogue or essentially functionally equivalent components with a difference of “100” (in Fig. 2) or by “200” (in Fig. 3) increased reference numbers.

[0041] With reference first to Fig. 2 comprises two ring disk elements 221, 222 for said manipulation in the z-direction or along the central axis 240, wherein the first of these ring disk elements 221 is assigned a tangential drive 207 for rotation about the central axis 240. The two ring disk elements 221, 222 have a double helix-shaped geometry on the mutually facing surfaces and are mounted on one another via a ball bearing 217 formed with a helical ball guide. This is shown in Fig. 2 is best seen in the position of the ball guide of the ball bearing 217 shown on the right in the illustration compared to the position of this ball guide shown on the left in the illustration. As a result of this configuration, a rotation of the annular disc element 221 about the central axis 240, induced by 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 displacement of the camera 250 along the z-axis.

[0042] The embodiment according to Fig. 2 has - in addition to the self-centering achieved by the existing ball bearings and direct force dissipation - the advantage of a particularly compact design and thus a space saving compared to the following with reference to Fig. 3 described (comparatively easier to manufacture) embodiment.

[0043] According to Fig. 3 includes, in contrast to Fig. 2 the second assembly 320, which is provided for providing the manipulability in the translational degree of freedom of displacement in the z-direction, has two wedge elements 321, 322, which according to Fig. 3 (and also in contrast to Fig. 2) is arranged below the first assembly or on its side facing away from the camera flange 351 and facing the base 330. Of these two wedge elements 321, 322, the first wedge element 321 is displaceably mounted via a linear drive 307 along an axis perpendicular to the center axis 340 (x-axis), as indicated by the horizontal double arrow, wherein corresponding ball bearings between the first wedge element 321 and the base 330 or between the first wedge element 321 and the second wedge element 322 are designated by "319" and "318", respectively. "314" designates a ball bearing between the second assembly 320 or its second wedge element 322 and the first assembly 310 or its first wedge-shaped annular disk 311. As in Fig. 3, the first wedge element 321 of the second assembly has an elongated hole to enable the said displacement of the first wedge element 321 in the direction perpendicular to the central axis 340.

[0044] The second wedge element 322 of the second assembly, unlike the first wedge element 321, is fixed in a direction perpendicular to the z-axis or center axis 340 (i.e. in the lateral plane) and is prevented from a corresponding lateral movement, as shown in Fig. 3 is symbolically indicated on the right by a stop 335. This has the consequence that during the above-described displacement of the first wedge element 321 along an axis perpendicular to the central axis 340 (x-axis), the said second wedge element 322 can only deflect in the direction along the z-axis, thereby achieving the desired translational z-displacement of the camera 350.

[0045] Fig.4 shows a schematic diagram to explain a possible basic structure of a mask inspection device. Accordingly, a mask inspection device comprises, in particular, an illumination system 450 and a projection lens 460, wherein an EUV beam path 445 emanating from an EUV radiation source 440 is guided via the illumination system 450 onto an EUV mask 470. The illumination system 450 shapes the EUV radiation into a beam bundle, which illuminates an examination field on the surface of the EUV mask 470 with uniform brightness. The illuminated area of ​​the mask 470 can, for example, have dimensions of 0.5 mm * 0.8 mm. The edge lengths of the EUV mask 470 can, for example, be between 100 mm and 200 mm. A field stop is arranged in the illumination system 450, with which the illuminated area is limited to the examination field on the surface of the EUV mask 470.Using a positioner 471, the EUV mask 470 can be moved in the horizontal plane to bring various examination fields into the range of the EUV beam path. The EUV mask 470 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, and be substantially rectangular in shape.

[0046] The EUV beam path 445 reflected by the EUV mask 470 continues via the projection lens 460 to an EUV camera 410 equipped with an image sensor 411. The projection lens 460 images the examination field of the EUV mask 470 onto the image sensor 411 of the EUV camera 410. The imaging beam path 445 impinges on the image sensor 411 in the z-direction. The EUV beam 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 system, a high vacuum is present in the vacuum chamber 430. The EUV camera 410 includes a camera housing 412 that supports the image sensor 411. A rear portion 413 of the camera housing 412 protrudes from the vacuum housing 406, while the image sensor 411 is exposed to the vacuum in the vacuum housing 406.

[0047] The EUV radiation source 440 is a plasma radiation source for generating EUV radiation with a wavelength of approximately 13.5 nm.

[0048] The mirrors of the illumination system 450 and the mirrors of 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 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. The projection lens 460 has a magnification factor of more than 100. In order to fully capture the image generated by the examination field of the EUV mask 470, the area of ​​the image sensor 411 is larger than the area of ​​the examination field, corresponding to the magnification factor. The image sensor 411 can, for example, have dimensions in the range of 100 mm to 200 mm.

[0049] Although the invention has been described with reference to specific embodiments, numerous variations and alternative embodiments will become apparent to those skilled in the art, e.g., by combining and / or interchanging features of individual embodiments. Accordingly, it will be understood by those skilled in the art that such variations and alternative embodiments are encompassed by the present invention, and the scope of the invention is limited only by the appended claims and their equivalents.

Claims

[1] Manipulable platform for mounting a camera (150, 250, 350) on a vacuum housing, with • a first assembly (110, 210, 310) which provides a first adjustment mechanism for tilting the platform, wherein the first assembly (110, 210, 310) has a first double wedge arrangement of two wedge-shaped annular discs (111, 112, 211, 212, 311, 312) which are rotatably mounted on one another about a predetermined axis via a first ball bearing (115, 215, 315). [2] Manipulable platform according to claim 1, characterized by that the two wedge-shaped ring discs (111, 112, 211, 212, 311, 312) match in their wedge angle. [3] Manipulable platform according to claim 1 or 2, characterized by that the first adjustment mechanism enables tilting of the platform about two axes orthogonal to each other and to the given axis. [4] Manipulable platform according to one of claims 1 to 3, characterized bythat the given axis is a center axis (140, 240, 340). [5] Manipulable platform according to one of the preceding claims, characterized by 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 predetermined axis. [6] Manipulable platform according to one of the preceding claims, characterized by that it has a second assembly (220, 320) which provides a second adjustment mechanism for the translational displacement of the platform along the predetermined axis. [7] Manipulable platform according to claim 6, characterized by that this second assembly (320) has a second double wedge arrangement consisting of two wedge elements (321, 322) which coincide in their wedge angle and are mounted on one another via a second ball bearing (318). [8] Manipulable platform according to claim 7, characterized by that a first wedge element (321) of these wedge elements is mounted displaceably via a linear bearing (319) along an axis perpendicular to the predetermined axis, this displacement being accompanied by a translational displacement of the second wedge element (322) of these wedge elements along the predetermined axis. [9] Manipulable platform according to claim 8, characterized by that the first wedge element (321) is assigned a linear drive (307) for displacing this first wedge element (321) along an axis perpendicular to the predetermined axis. [10] Manipulable platform according to claim 6, characterized by that the second assembly (220) has an arrangement of two annular disc elements (221, 222) whose mutually facing surfaces form a double helix-shaped geometry and which are mounted on one another via a ball bearing (216) with a helical ball guide. [11] Manipulable platform according to claim 10, characterized by that one of the ring disc elements (221) is assigned a tangential drive (207) for rotating the respective ring disc element (221) about the predetermined axis. [12] Manipulable platform according to one of the preceding claims, characterized by that the camera (150, 250, 350) is an EUV camera. [13] Mask inspection device, comprising a vacuum housing (406), an EUV camera (410) and a projection lens (460) arranged in a vacuum chamber (430) of the vacuum housing (406) for imaging at least a section of an EUV mask (470) onto an image sensor (411) of the EUV camera (410), characterized by that the EUV camera (410) is mounted on the vacuum housing (406) via a manipulable platform according to one of claims 1 to 12. [14] Method for adjusting a mask inspection device, wherein the mask inspection device has a vacuum housing (406), an EUV camera (410) and a projection lens (460) arranged in a vacuum chamber (430) of the vacuum housing (406) for imaging at least a section 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