Apparatus for inspecting an object pertaining to EUV semiconductor technology

Abstract

The invention relates to an apparatus (51) for inspecting an object (58) pertaining to EUV semiconductor technology comprising an illumination unit (67), an imaging optical unit (59) and a recording device (52) for imaging and capturing the object (58). The apparatus (51) is distinguished by the fact that for imaging the pupil illumination of the pupil plane (66) of the imaging optical unit (59), a Bertrand module (70, 71, 72,74) is arranged in a free space in the imaging optical unit (59).

Description

[0001] Apparatus for inspecting an object pertaining to EUV semiconductor technology

[0002] The present application claims the priority of the German patent application DE 10 2024 121 334.5 of July 26, 2024, the content of which is fully incorporated herein by reference.

[0003] The invention relates to an apparatus for inspecting an object pertaining to EUV semiconductor technology, in particular a mask inspection apparatus.

[0004] In semiconductor technology, various processes are combined for producing microstructured components, such as integrated circuits or LCDs (liquid crystal displays). The processes include, inter alia, the production and qualification of photolithographic masks, which are also referred to as photomasks or simply masks, the production of substrates, in particular wafers, and the qualification of substrates.

[0005] In the central so-called lithography process or microlithography process, the mask is illuminated in a projection exposure apparatus by an illumination unit. The light passing through the mask or the light reflected by the mask is projected, by means of a projection optical unit, onto a substrate (for example a wafer), which is coated with a light-sensitive layer (photoresist) and mounted in the image plane of the projection optical unit, in order to transfer the structure elements of the mask to the light-sensitive coating of the substrate. The structure transferred in this way to the substrate is formed in an electrically conductive material in a further process step. A microstructured component usually comprises between 20 and 50 of these layers, which cooperate to form a three-dimensional component. The process described above is thus repeated multiple times. A fault in just one layer can lead to the failure of the entire electrical component during production, which is why the masks and the wafers are checked for possible defects in inspection processes by means of so-called mask or wafer inspection apparatuses. In the case of masks, certain defects can be repaired in a subsequent step. For this purpose, the mask or wafer inspection apparatuses use microscopes which are specially designed for the application and which may also comprise, inter alia, a so-called Bertrand module.

[0006] A Bertrand module is a lens system, named after G.B. Amici and E. Bertrand and able to be switched on and off, between the objective, referred to as imaging optical unit, and the image plane, this lens system comprising a Bertrand element in the form of a lens or mirror. In semiconductor technology, the Bertrand module is used to check the pupil illumination of the imaging optical unit. To this end, the Bertrand lens, or in the case of an EUV semiconductor technology apparatus the Bertrand mirror, is slid or pivoted into the beam path of the microscope and images the pupil plane of the imaging optical unit onto a sensor, such as a camera. This makes it possible to check and possibly correct the position and illumination of the pupil plane of the imaging optical unit.

[0007] The Bertrand modules known from the prior art have the disadvantage that they are operated by means of actuators and / or kinematic systems that are affected by friction, as a result of which the very stringent requirements for EUV semiconductor technology apparatuses operated in a vacuum can no longer be met. Further disadvantages are the insufficient positioning accuracy with lens or mirror pivoted in and / or a Bertrand module construction that is too large for the available installation space owing to the kinematic system required for the positioning accuracy.

[0008] The international patent application WO 2017 153165 A1 discloses a switchable input coupling device of a measurement light source module of an EUV mask inspection apparatus, which is provided for coupling measurement light emitted by a measurement light source module into an illumination beam path of the mask inspection apparatus at an input coupling position upstream of a first facet mirror of an illumination unit. The measurement light source module contains a measurement light source for emitting measurement light from the visible spectral range. The input coupling device comprises a plane mirror, which serves as the input coupling mirror and which can be pivoted between a neutral position outside the illumination beam path and an input coupling position with the aid of an electric drive. In the case of the example, the measurement light source module generates an image of the measure- merit light source at the site of the source position (intermediate focus of the EUV radiation). The input coupling mirror can be pivoted such that the measurement light beam is coupled into the illumination beam path at the site of the source position as if the measurement light source MLS were located at the site of the source position. With this arrangement, it is thus possible to imitate or simulate the source beam present in EUV operation with the aid of measurement light.

[0009] US patent 10 712 287 B2 discloses an inspection apparatus for inspecting an EUV mask comprising a monitoring unit, which captures a luminance of illumination light of the inspection apparatus. For this purpose, part of the illumination light is reflected from a separating mirror to a detector. The monitoring unit can thereby capture the luminance of the illumination light and output the luminance data of the illumination light, said data being captured by the detector for the correction of the illumination light, to a processing unit of the inspection apparatus. This has the disadvantage that only part of the illumination light is coupled out. This light coupled out at the edge of the illumination light also includes edge effects, and so a sufficiently accurate conclusion regarding a distribution of the illumination light cannot be determined.

[0010] The European patent application EP 0628806 A2 discloses an optical system which involves exchanging a Bertrand module for imaging the pupil illumination for an optical element of the imaging optical unit of a mask inspection apparatus. This has the disadvantage that at least one optical element of the imaging optical unit is removed from the system and integrated again. Even if the optical element is pivoted in and out again by a device, the imaging quality will change owing to the tolerances of pivoting out and in, which adversely affects the reproducibility of the measurement results.

[0011] It is an object of the present invention to provide an apparatus which eliminates the disadvantages of the prior art elucidated further above.

[0012] This object is achieved by an apparatus having the features of independent claim 1 . The dependent claims relate to advantageous developments and variants of the invention. An apparatus according to the invention for inspecting objects pertaining to EUV semiconductor technology comprising an illumination unit, an imaging optical unit and a recording device for imaging and capturing an object is distinguished by the fact that for imaging the pupil illumination of the pupil plane of the imaging optical unit, a Bertrand module is arranged in a free space in the imaging optical unit.

[0013] Free space in the sense of the invention is taken to mean a volume which is not occupied or used by any other component of the apparatus and which may also be referred to as a free installation space. This makes it possible to capture the pupil illumination without changing the positions of the optical elements of the imaging optical unit. This prevents a change in the imaging quality owing to changes in position that possibly occur during pivoting-out and once again pivoting-out of an optical element of the imaging optical unit owing to tolerances present in the mechanism.

[0014] Within the meaning of the invention, the imaging optical unit of the inspection apparatus comprises both the imaging part, which fulfills the function of the imaging of the object, and the magnifying part, which only magnifies the imaging of the object and is referred to as a tube.

[0015] In particular, the Bertrand module can be arranged in such a way that at least one optical element of the imaging optical unit is at least partly shaded by the Bertrand module. This has the advantage that further optical elements of the imaging optical unit can be used for capturing the pupil illumination on the recording device. The Bertrand module can be arranged upstream of one of four mirrors of the imaging optical unit, for example, and the downstream mirrors in the beam path of the apparatus can still be used for imaging the pupil onto the recording device.

[0016] In a further embodiment of the invention, the Bertrand module can be arranged in such a way that the pupil plane of the imaging optical unit is imaged at least onto a part of the recording device. The pupil plane formed in or directly in the vicinity of the pupil stop can also be imaged by way of a Bertrand module in the further course of the beam path after the pupil stop and possible further optical elements. This has the advantage that the beams often have a significantly smaller beam diameter or horizontal extent, as a result of which the optical elements which are used in the Bertrand module and which are embodied as mirrors in EUV semiconductor technology can be designed in a more compact way. As a consequence, the imaging can also be significantly smaller than that of the object during operation of the apparatus, such that the use of only a part of the recording device is made possible. Especially in the case of a recording device in the form of a multi-array sensor, this has the advantage that just one array can be used for capturing the pupil illumination. This can result in a higher accuracy, since no gaps filled by interpolation are present in the imaging.

[0017] Alternatively, the Bertrand module can be arranged in such a way that the pupil plane is imaged onto an additional recording device. This has the advantage that the recording device can be designed for the requirements in respect of the imaging of the pupil plane.

[0018] In a further embodiment of the invention, the Bertrand module can comprise at least one optical Bertrand element.

[0019] Furthermore, the Bertrand module can comprise two optical Bertrand elements.

[0020] In particular, the Bertrand element can be embodied as an EUV mirror.

[0021] In a further embodiment of the invention, the Bertrand module can comprise at least one mirror of the imaging optical unit for imaging the pupil illumination of the imaging optical unit. In other words, the imaging of the pupil plane is generated by at least one Bertrand element embodied as a mirror and at least one mirror of the imaging optical unit of the apparatus.

[0022] In a further embodiment of the invention, the apparatus can comprise a device for introducing a Bertrand element into a beam path of the apparatus for EUV semiconductor technology. In particular, the Bertrand element can be an element as outlined above, namely an EUV mirror.

[0023] The device can comprise in particular a device for pivoting an optical component into a beam path of an apparatus for semiconductor technology and can comprise a pivoting arm and the Bertrand element arranged on the pivoting arm. Furthermore, the device can comprise at least one rotary joint, by way of which the pivoting arm is pivotally mounted in the device, wherein at least one rotary joint is in the form of a flexure. The flexure allows the optical module, which can for example be in the form of a Bertrand module, to be pivoted in over a large angle of rotation with a comparatively high accuracy and small installation space requirement. Furthermore, a flexure of elastic design exhibits no hysteresis and no stick-slip effects, as a result of which a very high accuracy and reproducibility can be achieved.

[0024] In contrast to a rotary joint, in the case of a flexure a rotational movement is effected by the deformation, usually bending, of a generally elastic region of the joint. Typical representatives of flexures are, for example, film hinges. In contrast to typical rotary joints, in the case of flexures no surfaces slide on one another, with the result that no lubrication is required and furthermore also no particle abrasion by the actuation of the joint is caused.

[0025] In particular, the angle of rotation of the rotary joint during the pivoting-in can be at least 27°, preferably at least 28°, particularly preferably at least 30°. The comparatively large angle of rotation is due to the fact that, owing to the high cleanness requirements for protecting the optical elements in semiconductor technology apparatuses, in particular for EUV semiconductor technology, in principle all the components which by friction, outgassing by used materials, such as by a kinematic system and / or actuator system, or other contaminating causes have to have the greatest possible distance from the optical elements of the semiconductor technology apparatuses. In particular, such components must not be arranged within a region, referred to as mini environment, directly around the optical elements. At the same time, in a parking position of the optical module pivoted into the beam path only for measurement purposes, the beam path relevant for the measurement of the substrates, such as masks or wafers, must not be restricted by any component of the device.

[0026] In a further embodiment of the invention, the flexure can comprise at least two elastic subregions.

[0027] In particular, the at least two elastic subregions can be connected by way of flexurally rigid connecting elements, thereby producing a folded leaf spring, the action of the individual elastic subregions thereof adding up to form a total length. In a first approximation, this can correspond to a conventional leaf spring with a corresponding total length. If a plurality of elastic subregions are connected to one another by means of flexurally rigid connecting elements in the form of deflections, the deflections having an angle of 180°, the leaf spring can adopt a meandering shape. As an alternative, any other conceivable folding of the leaf spring of equal total length can have a comparable elastic action. The folding of the leaf spring has the advantage that a comparatively large angle of rotation can be realized in a comparatively compact installation space.

[0028] Furthermore, the summed length of the elastic subregions can be at least 450 mm, preferably at least 460 mm and particularly preferably at least 480 mm.

[0029] In a further embodiment of the invention, the center of gravity of the pivoting arm of the device can lie on the axis of rotation of the at least one rotary joint, as a result of which advantageously it is not necessary to take account of any displacement of the position of the optical module through the center of gravity when positioning the arm.

[0030] In particular, the pivoting arm can comprise interchangeable balancing weights for displacing the center of gravity of the pivoting arm, in particular in the axis of rotation of the rotary joint, after the device has been mounted. The pivoting arm can thus be adjusted in such a way that the position relevant for the functioning of the optical module is maintained on the z-axis parallel to the axis of rotation during the rotational movement.

[0031] In a further embodiment of the invention, the device can comprise a fixing device of the pivoting arm in a measurement position of the pivoting arm. On the one hand, the fixing device can stiffen the tilting rigidity of the axis of rotation of the at least one torsion spring in the direction of the longitudinal extent of the pivoting arm. On the other hand, further degrees of freedom, in particular the translational degrees of freedom, in which the flexure is comparatively pliant owing to its design, can also stiffen. On the other hand, the fixing device can ensure that the position of the optical module is maintained at a predetermined position.

[0032] The fixing device can, for example, comprise a magnet, in particular an electromagnet. The magnet is positioned in a region in which the pivoting arm lies in a predefined measurement position. In the case of the electromagnet, the latter can be activated after the pivoting arm has been positioned and fix the pivoting arm in this position. The magnet thus has to apply a predefined force in dependence on the additionally required stiffening of the system. In addition to an increase in the strength of the magnetic field that can be generated by the magnet, the distance between the magnet and the pivoting arm can additionally also be reduced in order to increase the magnetic force. In this case, the distance can be smaller than 1 mm, preferably smaller than 0.5 mm and particularly preferably smaller than 0.2 mm.

[0033] Furthermore, the pivoting arm can comprise an anchor plate for fixing the pivoting arm with the magnet. The anchor plate expediently comprises a magnetizable material, as a result of which the pivoting arm, which on the basis of weight can usually be produced from a nonmagnetic material, in particular from aluminum, can be fixed by the magnet.

[0034] As an alternative, further embodiments for the fixing device are conceivable, such as a mechanical clamp with an adjustable stop, against which the pivoting arm can be pressed and thus clamped for example by an actuator.

[0035] In a further embodiment of the invention, the device can comprise an actuator for deflecting the pivoting arm, which can be designed to pivot the pivoting arm from a parking position into a measurement position and back.

[0036] Furthermore, a force transmission element of the actuator with the rotary joint can be designed in such a way that the actuator can transmit only tensile forces to the pivoting arm. The actuator can thus pull the pivoting arm out of the measurement position into a parking position, the at least one rotary joint being preloaded. When pivoting the pivoting arm back in, the restoring force of the rotary joint acts, such that the actuator does not exert any force on the pivoting arm. This has the advantage that, during the positioning of the pivoting arm, which as elucidated above is defined by the fixing, there is no overdetermination by way of a rigid force transmission element of the actuator. The force transmission element, which is pliant in the pressure direction, advantageously reduces the force acting on the pivoting arm from the actuator in the measurement position to a value that is irrelevant for the positioning. In a further embodiment of the invention, the at least one rotary joint in a measurement position of the pivoting arm can be arranged in such a way that it has no or virtually no deflection from its force-free zero deflection. The zero deflection is the deflection at which the leaf spring of the joint is free of stress, as no energy in the form of a preload is stored in the spring. As a result of the stress-free leaf spring, the rotary joint cannot cause any parasitic force on the pivoting arm. This has the advantage, on the one hand, that deformations caused by parasitic force do not influence the positioning of the pivoting arm and, on the other hand, possible deformation of the optical module and of the optical element held therein can be avoided. In combination with the connection of the actuator to the arm as elucidated above, the pivoting arm is held in a virtually force-free manner at least in its predetermined direction of rotation in the measurement position.

[0037] In a further embodiment of the invention, the device can comprise two rotary joints in mirror-inverted form with a common axis of rotation. The mirror-inverted form is necessary, since a rotary joint rotated through 180° would have the effect that one rotary joint is preloaded through the angle of rotation and the other is not. The opposed restoring forces of the rotary joints would cancel each other out and the restoring force elucidated above for pivoting in the pivoting arm and in particular the virtually low-stress state of the rotary joints in the measurement position would no longer be realized.

[0038] In particular, the distance between the two rotary joints arranged in mirror-inverted fashion can be at least 43 mm, preferably at least 45 mm, particularly preferably at least 50 mm.

[0039] The device can be regarded as an independent invention and is not restricted to the introduction of a Bertrand element into a free space and / or to an apparatus for inspecting objects pertaining to EUV semiconductor technology. In particular, the apparatus can be embodied as a mask inspection apparatus, as a mask repair apparatus, as a microscope, as a projection exposure apparatus or as a wafer inspection apparatus. Exemplary embodiments and variants of the invention are explained in greater detail below with reference to the drawing, in which: figure 1 shows a schematic illustration of a Bertrand module according to the invention, figure 2 shows a detail of the invention, figures 3a, b show a further detail of the invention, figures 4a, b show a further detail of the invention, figure 5 shows a schematic illustration of a mask inspection apparatus known from the prior art, and figure 6 shows a further embodiment of the invention.

[0040] Figure 1 shows a schematic illustration of a Bertrand module 1 , which comprises a housing 2 with a box 3 and a pivoting arm 5.1 , 5.2 projecting from the box 3. Here, the reference sign 5.1 represents the pivoting arm in a measurement position and the reference sign 5.2 represents the pivoting arm in a parking position, which is illustrated in dashed form in figure 1 . The box 3 is connected to an attachment 4 which can be used to arrange the housing 2 for example in a mask inspection apparatus 31 , as is elucidated in detail in figure 5. The reference signs 6.1 , 6.2 denote the longitudinal axes of the pivoting arm 5.1 , 5.2.

[0041] The pivoting arm 5.1 , 5.2 is mounted in the housing 2 and designed to be rotatable about an axis of rotation 7. The rotation of the pivoting arm 5.1 , 5.2 allows the pivoting arm 5.1 , 5.2 to move out of the parking position into the measurement position, which is illustrated by solid lines in figure 1 . In the embodiment illustrated in figure 1 , the angle of rotation a through which the pivoting arm 5.1 , 5.2 can be pivoted out of the measurement position into the parking position and vice versa lies in a range from 20° to 30°, it also being possible to realize smaller and in particular larger angles of rotation a. Arranged at the free end of the pivoting arm 5.1 , 5.2 is an optical element which in the embodiment illustrated in figure 1 is in the form of a Bertrand mirror 8, 70.1 , 71 .1 , 71.2, 72.1 and is held by a mirror holder 9 connected to the pivoting arm 5.1 , 5.2.

[0042] The Bertrand mirror 8, 70.1 , 71 .1 , 71 .2, 72.1 pivoted into the beam path 43, 44 of the mask inspection apparatus 31 (figure 5) has the effect that the pupil of the imaging optical unit 39 of the mask inspection apparatus 31 is imaged onto a sensor, such as a camera 32. This makes it possible for the pupil illumination to be checked and, if necessary, adapted.

[0043] The pivoting arm 5.1 is connected, by way of a force transmission element 15 (figure 4) which is not visible in figure 1 , to an actuator 23 (figure 4) which is also not visible and moves the pivoting arm 5.1 out of the measurement position into the parking position, illustrated in dashed form in figure 1 , of the pivoting arm 5.2.

[0044] The housing 2 of the device 1 and thus all the components of the device 1 which potentially contribute to contamination of the optical elements are virtually completely closed off from the surroundings by the box 3 and are arranged, as a result of the comparatively long pivoting arm 5.1 , 5.2, at a sufficient distance that the risk of contamination of the optical element of the imaging optical unit 39 (figure 5) is reduced to a non-critical level.

[0045] Figure 2 shows a portion of the device 1 in the form of a Bertrand module, in which the pivoting arm 5.1 is illustrated in the measurement position. The box 3 shown in figure 1 is not illustrated in figure 2, with the result that a support 16 of the pivoting arm 5.1 is readily visible. The support 16 comprises two torsion springs 10.1 , 10.2 which define the axis of rotation 7 of the pivoting arm 5.1. In the illustration in figure 2, only the torsion spring 10.1 can be seen, the second torsion spring 10.2 is hidden by other components.

[0046] The torsion springs 10.1 , 10.2 each comprise two spring shells 17.11 , 17.12, 17.21 , 17.22, which in each case correspond to an end of the torsion springs 10.1 , 10.2, wherein only the spring shell 17.11 can be seen in the illustration in figure 1 . Arranged between the spring shells are folded leaf springs 19.1 , 19.2 which are elucid- ated in detail in figure 3a, wherein only the leaf spring 19.1 of the torsion spring 10.1 can be seen in figure 2.

[0047] The torsion springs 10.1 , 10.2 are arranged in the device 1 in such a way that the torsion springs 10.1 , 10.2 are preloaded in the parking position of the measuring arm 5.2, whereas the torsion springs 10.1 , 10.2 in the measurement position of the pivoting arm 5.1 have no or virtually no preload. The restoring force of the torsion springs

[0048] 10.1 , 10.2 can thus bring about the rotational movement of the pivoting arm 5.1 , 5.2 out of the parking position into the measurement position.

[0049] The torsion springs 10.1 , 10.2 are, on one side, connected to the attachment 4 by means of one spring shell 17.11 , 17.21 and to the pivoting arm 5.1 by means of the other spring shell 17.12, 17.22. Both connections are realized by a clamping connection 11.1 , 11.2, 13.1 , 13.2 in the embodiment illustrated in figure 2. In this case, the outer diameters of the spring shells 17.11 , 17.12, 17.21 , 17.22 are clamped in clamping jaws 12.11 , 12.12, 12.21 , 12.22, 14.1 , 14.2 of the clamping connections 11.1 ,

[0050] 11.2, 13.1 , 13.2. The spring shells 17.11 , 17.21 which are further away from the longitudinal axis 6.1 of the pivoting arm 5.1 are in this case connected to the attachment 4, and the spring shells 17.12, 17.22 which are arranged closer to the longitudinal axis 6.1 of the pivoting arm 5.1 are connected to the pivoting arm 5.1 . The torsion springs 10.1 , 10.2 and the connection thereof to the pivoting arm 5 are elucidated in detail in figure 3a and figure 3b.

[0051] During mounting, the springs 10.1 , 10.2 are preloaded in such a way that a minimum restoring force remains when the measurement position of the pivoting arm 5.1 is reached. This is necessary in order to ensure that, in spite of the tolerances that differ from device to device, the measurement position is always reached as a result of the energy stored in the torsion springs 10.1 , 10.2. This minimum residual preload is effected by deflecting the springs 10.1 , 10.2 through 1 ° in relation to the direction of the longitudinal axis 6.1 of the pivoting arm. To this end, when mounting the device 1 , those spring shells 17.12, 17.22 (not visible) of the torsion springs 10.1 , 10.2 which are directed toward the arm 5.1 are first aligned, by way of positioning bores 18.11 , 18.21 located in clamping jaws 14.1 , 14.2 of the pivoting arm 5.1 , with corresponding bores 18.12, 18.22 (figure 3a) in the spring shells 17.12, 17.22 and clamped in this position. The rotary joint 10.1 is thus connected to the pivoting arm 5.1 in a manner rotated through 1 ° in relation to the direction of the longitudinal axis 6.1 of the pivoting arm 5.1 .

[0052] During the subsequent mounting of the spring shells 17.11 , 17.21 facing away from the arm 5.1 with the attachment 4, during clamping with the clamp 11.1 , 11.2, said shells are pulled, by way of a flattened portion on the outer diameter of the spring shells 17.11 , 17.21 , onto corresponding surfaces on the attachment 4, as a result of which the spring shells 17.11 , 17.21 no longer have a deflection in relation to the longitudinal axis 6.1 of the pivoting arm 5.1 .

[0053] The spring shells 17.11 , 17.21 , 17.12, 17.22 are thus mounted in a manner rotated through 1 ° relative to one another, such that they are still deflected through 1 ° in the measurement position of the pivoting arm 5.1 , or, in other words, without a stop or a fixing device 25 elucidated in more detail in figure 4b, the pivoting arm 5.1 would be deflected through 1 ° beyond the desired measurement position.

[0054] Figure 3a shows a torsion spring 10.1 with a spring shell 17.11 and a spring shell 17.12 which are connected to one another by way of a leaf spring 19.1 formed from a plurality of elastic subregions 19.11. The torsion spring 10.1 is clamped with the attachment 4 (figure 2) by way of the spring shell 17.11 , as elucidated in figure 2, and clamped with the pivoting arm 5 by way of the spring shell 17.12.

[0055] In the embodiments shown in the figures, the leaf spring 19.1 is of meandering design, in other words the individual elastic subregions 19.11 alternate with connecting elements of the leaf spring 19.1 which are in the form of flexurally rigid deflections 20.1 , 20.2, wherein, for reasons of clarity, only one elastic subregion 19.11 is denoted by a reference sign in figure 3a. Rotation of the spring shells 17.11 , 17.12 relative to one another causes the deflections 20.1 , 20.2 of the leaf spring 19.1 on one side to move toward one another and on the other side to move away from one another, such that the leaf spring 19.1 in the deflected state is of fan-like design. In this case, the distance between the deflections 20.1 , 20.2 is selected in such a way that they do not touch in the case of a rotational deflection of the leaf spring 19.1 over the predetermined angle range, which is at most 30° in the embodiment elucidated in fig- ure 3a, which would equate to bottoming out of a spiral spring. In all further degrees of freedom, the torsion spring 10.1 is designed to be more rigid in comparison with the torsional rigidity about the axis of rotation 7, wherein in particular the degree of freedom oriented perpendicularly to the longitudinal orientation of the leaf spring 19.1 is comparatively pliant by compression or pulling-apart of the individual leaf spring portions 19.11. In order to avoid plastic deformation of the leaf spring 19.1 , the compression is limited by contact of the leaf spring portions 19.11 or of the deflections

[0056] 20.1 which is comparable to the bottoming out of a spiral spring, and the pulling-apart is limited by the spring shells 17.11 , 17.21 surrounding the leaf springs 19.1 . The further rotational degrees of freedom about the axes perpendicular to the axis of rotation 7 are blocked by the clamping of the spring shells 17.11 , 17.12, 17.21 , 17.22 which are spaced apart from one another and are not permitted to rotate as a result of the fixed clamping. In addition, the rigidities of the leaf spring 19.1 are several times higher over its width and height in comparison to the thickness.

[0057] Figure 3b shows a further detail of the invention, the clamp 13.1 , 13.2 for the torsion springs 10.1 , 10.2 on the pivoting arm 5 being illustrated. The torsion springs 10.1 ,

[0058] 10.2 are positioned in mirror-inverted fashion relative to one another, as a result of which both torsion springs 10.1 , 10.2 are preloaded in the parking position, that is to say have a restoring force, and virtually no longer have any restoring force in the measurement position, as elucidated further above.

[0059] The center of gravity 21 of the pivoting arm 5 is designed in such a way that it lies on the common axis of rotation 7 of the rotary joints 10.1 , 10.2. This has the advantage that the contribution to the tilting of the pivoting arm 5 on account of gravity is very small or may even be zero. In order to compensate for manufacturing tolerances which may lead to a displacement of the center of gravity 21 of the pivoting arm 5, balancing masses 22 are arranged on the left-hand side in figure 3b, which are used to orient the center of gravity 21 on the axis of rotation 7 of the rotary joints 10.1 , 10.2.

[0060] Figure 4a shows a further detail of the invention, the pivoting arm 5.1 being illustrated in the measurement position with the actuator 23 which is used to deflect the pivoting arm 5.1 out of the measurement position into a parking position. The actuator 23 is connected to the pivoting arm 5.1 by way of a force transmission element 15, wherein the force transmission element 15 can transmit only a tensile force to the pivoting arm 5.1. The actuator 23 thus pulls the pivoting arm 5.1 counter to the spring rigidity of the torsion springs 10.1 , 10.2 from the measurement position into the parking position of the pivoting arm 5.2. In the reverse movement out of the parking position into the measurement position, the actuator 23 is moved, the pivoting arm 5 being moved by the restoring force present in the torsion springs 10.1 , 10.2. During the movement into the measurement position and in particular when the measurement position is reached, the actuator 23 can exert no or only a negligible force on the pivoting arm 5.1 by way of the force transmission element 15. In the measurement position, the pivoting arm 5.1 is thus virtually free of parasitic forces, both by the actuator 23 and by the torsion springs 10.1 , 10.2.

[0061] The actuator 23 is connected to a controller (not illustrated) by way of a line 24. The actuator 23 can have a sensor (not illustrated) for ascertaining the displacement travel, by means of which the position of the pivoting arm 5.1 , 5.2 can be ascertained.

[0062] Figure 4b shows a further detail of the invention, a portion of the pivoting arm 5 with the support 16 and a fixing device 25 for fixing the pivoting arm 5.1 in its measurement position being illustrated.

[0063] In the embodiment illustrated in figure 4b, the fixing device 25 comprises an electromagnet 26 which pulls the pivoting arm 5.1 against the fixing device 25 when the measurement position is reached. Owing to the nonmagnetic aluminum used for the pivoting arm 5.1 , a magnetizable anchor plate 27 is embedded in the pivoting arm 5.1 in the region of the electromagnet 26. The distance between the electromagnet 26 and the anchor plate 27 is in this case only a few tenths of a millimeter, such that the movement of the mirror 8, 70.1 , 71 .1 , 71 .2, 72.1 (figure 1 ) via the movement of the pivoting arm 5.1 can be ignored. As an alternative, the device 1 can be adjusted to the extent that the position of the mirror 8, 70.1 , 71 .1 , 71 .2, 72.1 when the electromagnet 26 is switched on corresponds to the previously determined position. The fixing of the pivoting arm 5.1 by way of the fixing device 25 brings about a higher rigidity of the support 16 in all six degrees of freedom, as a result of which an excitation of the pivoting arm 5.1 by parasitic mechanical vibrations, for example from other com- ponents of the overall system or from the surroundings, during the measurement can advantageously be reduced. The positioning of the pivoting arm 5.1 , 5.2 in the measurement position or parking position can be regulated as elucidated further above either by way of a sensor (not illustrated) mounted on the actuator 23 for regulating the displacement travel of the actuator 23 or by an external sensor (not illustrated) which detects the rotational position of the pivoting arm 5.1. As an alternative, the measurement position of the pivoting arm 5.1 can also be defined by a settable mechanical stop or a light barrier which is set in such a way that, when the light barrier is triggered, the pivoting arm 5.1 is in the previously determined rotational position and is fixed in said position by the fixing device 25.

[0064] Figure 5 shows a schematic illustration of a mask inspection apparatus 31 for measuring an object 38, which can for example be in the form of a photomask. The mask inspection apparatus 31 comprises two light sources 34, 35, a first light source 34 being designed for a measurement of the object 38 in reflection and a second light source 35 being designed for a measurement of the object 38 in transmitted light.

[0065] The object 38 is arranged on an object stage 37, which can position the object 38 laterally and vertically in the sub-nanometer range. In this case, the positional accuracy can be in particular in a range of less than 100 nm, in particular less than 20 nm. During a transmitted-light measurement, the measurement light 44 of the illumination unit 47, which comprises the light source 35 and an illumination optical unit in the form of a condenser 36, passes through the condenser 36, which generates a desired light distribution on the object 38. The pupil plane of the illumination optical unit 36 is denoted by the reference numeral 46 in the figure. The measurement light 44 passes further through the object 38, which is subsequently imaged by an imaging optical unit 39 and a tube 41 . The tube 41 magnifies the imaging of the object 38 and images it in turn onto a recording device 32 in the form of a CCD camera. The semitransparent mirror 40 arranged between the imaging optical unit 39 and the tube 41 is used for the measurement in reflection and has no influence on the measurement in transmitted light.

[0066] During a measurement in reflection, the measurement light 43 emitted by the light source 34 is reflected at the semitransparent mirror 40 and then impinges on the ima- ging optical unit 39. The latter focuses the measurement light 43 on the object 38, from which it is reflected. The measurement light 43 passes once more through the imaging optical unit 39 and the latter images the object 38 through the semitransparent mirror 40 on the tube 41 . The tube 41 magnifies the imaging of the object 38 and images it onto the recording device 32.

[0067] In order to check and / or adjust the imaging optical unit 39, it is optionally possible for a Bertrand module 1 , which for example comprises a so-called Bertrand element in the form of a Fresnel zone plate (mirror 8, 70.1 , 71 .1 , 71 .2, 72.1 - figure 1 ), to be pivoted into the beam path of the mask inspection apparatus 31 between the recording device 32 and the tube 41 , the device 1 elucidated in figures 1 to 4 being able to be used for this. This has the effect that what is imaged onto the recording device 32 is no longer the object 38, but rather the pupil 45 of the imaging optical unit 39. The pupil 45 comprises the influences of all the optical components involved in the imaging, that is say in particular the condenser 36 and / or the imaging optical unit 39, such that a predetermined pupil illumination in the pupil 45 can be set by adjustment of the optical components 36, 39, in particular of the imaging optical unit 39, and / or further components which have an effect on the pupil illumination, such as the illumination unit 47.

[0068] As an alternative, the Bertrand module 1 can also be pivoted in between the imaging optical unit 39 and the tube 41 , since these are arranged in a manner mechanically separated from one another and the requisite free space is afforded.

[0069] In cases in which the object 38 is in the form of a photomask, the latter can 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. The photomask can be configured in substantially rectangular fashion. The photomask can preferably have a length and width of 5 to 7 inches, particularly preferably a length and width of 6 inches. As an alternative thereto, the photomask can have a length of 5 to 7 inches and a width of 10 to 14 inches, preferably a length of 6 inches and a width of 12 inches.

[0070] Figure 6 shows a schematic illustration of an apparatus, in the form of an EUV mask inspection apparatus 51 , for measuring an object 58, which can be embodied as a photomask, for example. In principle, the mask inspection apparatus 51 has the same features as the mask inspection apparatus 31 described in figure 5, and, where practical, identical features are designated by the same reference sign increased by 20.

[0071] The mask inspection apparatus 31 in figure 5 comprises a dedicated imaging optical unit 39 having an internal pupil and a tube 41 for subsequent magnification. As a result, there is a natural engagement position downstream of the imaging optical unit 39 or, as elucidated in figure 5, downstream of the tube 41 , since here there is enough free space, i.e. installation space not required by other components of the mask inspection apparatus 31 .

[0072] In the mask inspection apparatus 51 , the optical functionalities of the imaging optical unit 59 and of the tube 61 are no longer clearly mechanically separated, which can also be explained by the purely reflective optical system. The mirrors M1 and M2 perform the function of the imaging optical unit 59 and the mirrors M3 and M4 perform the function of the tube 41 . The further functioning of the mask inspection apparatus 51 is identical to the mask inspection apparatus 31 and will therefore not be elucidated again here.

[0073] The embodiment of the apparatus 51 that is elucidated in figure 6 has four possible positions for arranging an additional Bertrand module 70, 71 , 72, 74. The Bertrand module 70, 71 , 72, 74 comprises a Bertrand element 70.1 , 71 .1 , 71 .2, 72.1 , 74.1 and a device 1 for introducing the Bertrand element 70.1 , 71 .1 , 71 .2, 72.1 , 74.1 into the imaging optical unit 59 or the tube 61 . For reasons of clarity, a device 1 is depicted only for the Bertrand module 70 in figure 6.

[0074] The Bertrand module 70, 71 , 72, 74 images the pupil 66 of the imaging optical unit 59 at the respective recording device 52, 73, 75.

[0075] In the embodiment illustrated in figure 6, the preferred position for a Bertrand module 70 is just beneath the mirror M3 of the imaging optical unit 59 or the tube 61 . The position has the advantage that only one Bertrand element in the form of a mirror 70.1 is required in the Bertrand module 70 for the purpose of imaging the pupil 66 onto the recording device 52 of the mask inspection apparatus 51 . By virtue of the comparat- ively small imaging size of the pupil 66 on the recording device 52, in the case of a multi-array sensor as recording device 52, the imaging can be imaged onto just one array, as a result of which a higher resolution can be achieved since there are no gaps in the capture of the imaging. The Bertrand module 70 uses the mirror M4 of the imaging optical unit 59 or of the tube 61 for imaging the pupil 66.

[0076] A further possible alternative position is the position of the Bertrand module 71 , which is likewise arranged just beneath the mirror M3 of the imaging optical unit 59 or the tube 61 . However, the Bertrand module 71 uses two Bertrand elements in the form of mirrors 71 .1 , 71 .2 for imaging the pupil 66, the recording device 52 of the mask inspection apparatus 51 likewise being used as recording device 52 of the Bertrand module 71. No further mirror M4 of the imaging optical unit 59 or of the tube 61 is used for imaging the pupil 66. This has the advantage that the imaging of the pupil can be optimized with two freely designable mirrors 71.1 , 71.2. Adverse factors are the higher production costs of an additional mirror 71 .2 and the free space additionally required in the imaging optical unit 59.

[0077] A further possible alternative position is the position of the Bertrand module 72, which is likewise arranged between mirrors M2 and M3 of the imaging optical unit 59 or the tube 61 . In the embodiment illustrated in figure 6, the Bertrand module 72 is arranged closer to the center between mirror M2 and mirror M3. In addition to having a Bertrand element in the form of a mirror 72.1 , the Bertrand module 72 has a separate recording device 73 for the pupil 66. Owing to the position of the Bertrand module 72 with respect to the mirror M4, the latter cannot be used for imaging the pupil 66 onto the recording device 52 of the mask inspection apparatus 51 , and so the additional separate recording device 73 becomes necessary.

[0078] The separate recording device 73 has the advantage that it can be optimized for capturing the pupil 66.

[0079] A further alternative position is the position of the Bertrand module 74, which is arranged between mirror M1 and the pupil 66. The Bertrand module 74 comprises additional to the mirror 74.1 , which acts as Bertrand element, a separate recording device 75 for the pupil 66. Owing to the position of the Bertrand module 74 in relation to the mirror M4, the mirror M4 cannot be used for imaging the pupil 66 on the recording device 52 of the mask inspection apparatus 51. As a consequence, the additional recording device 75 is necessary.

[0080] The separate, additional recording device 75 has the advantage that it can be optim- ized for the recording of the pupil 66.

[0081] The Bertrand modules 70, 71 , 72, 74 can comprise a device elucidated in figures 1 to 4, although the Bertrand modules 70, 71 , 72, 74 can also comprise any other device that satisfies the requirements for introducing the Bertrand element 70.1 , 71 .1 , 71 .2, 72.1 , 74.1 into the beam path of the imaging optical unit 59 or the tube 61 .

[0082] List of reference signs

[0083] 1 Bertrand module

[0084] 2 Housing

[0085] 3 Box

[0086] 4 Attachment for the mask inspection apparatus

[0087] 5, 5.1 , 5.2 Pivoting arm

[0088] 6, 6.1 , 6.2 Longitudinal axis of the pivoting arm

[0089] 7 Axis of rotation of the pivoting arm

[0090] 8 Mirror

[0091] 9 Mirror holder

[0092] 10.1 , 10.2 Torsion spring

[0093] 11.1 , 11.2 Clamp for the torsion spring-attachment

[0094] 12.11 , 12.12, 12.21 , 12.22 Clamping jaw / receptacle-attachment

[0095] 13.1 , 13.2 Clamp for the torsion spring-pivoting arm

[0096] 14.1 , 14.2 Clamping jaw of the pivoting arm

[0097] 15 Force transmission element for the actuator-pivoting arm

[0098] 16 Support

[0099] 17.11 , 17.12, 17.21 , 17.22 Spring shells

[0100] 18.11 , 18.12, 18.21 , 18.22 Positioning bore in the spring shell and pivoting arm

[0101] 19.1 , 19.2, 19.11 Leaf spring, subregions of the leaf spring

[0102] 20.1 , 20.2 Deflection of the leaf spring

[0103] 21 Center of gravity of the pivoting arm

[0104] 22 Balancing weights for the center of gravity of the pivoting arm

[0105] 23 Actuator

[0106] 24 Line

[0107] 25 Fixing device

[0108] 26 Electromagnet

[0109] 27 Anchor plate

[0110] 31 Mask inspection apparatus

[0111] 32 Recording device

[0112] 34 Light source for reflected-light measurement

[0113] 35 Light source for transmitted-light measurement

[0114] 36 Illumination optical unit

[0115] 37 Object stage

[0116] 38 Object

[0117] 39 Imaging optical unit

[0118] 40 Mirror

[0119] 41 Tube

[0120] 42 Controller

[0121] 43 Measurement light for reflected-light measurement

[0122] 44 Measurement light for transmitted-light measurement

[0123] 45 Pupil plane of imaging optical unit

[0124] 46 Pupil plane of condenser

[0125] 47 Illumination unit

[0126] 51 Mask inspection apparatus 52 Recording device of apparatus

[0127] 53 Bertrand mirror

[0128] 54 Light source for reflected-light measurement

[0129] 56 Illumination optical unit

[0130] 57 Object stage

[0131] 58 Object

[0132] 59 Imaging optical unit

[0133] 60 Mirror

[0134] 61 Tube

[0135] 62 Controller

[0136] 63 Measurement light for reflected-light measurement

[0137] 66 Pupil

[0138] 67 Illumination unit

[0139] 70, 70.1 Bertrand module / mirror

[0140] 71 , 71.1 , 71.2 Bertrand module / mirror

[0141] 72, 72.1 Bertrand module / mirror

[0142] 73 Recording device for Bertrand mirror

[0143] A Angle of rotation of the pivoting arm

[0144] 74 Bertrand Module

[0145] 74.1 Mirror

[0146] 75 Recording device

Claims

1. Patent claims1 . An apparatus (51) for inspecting an object (58) pertaining to EUV semiconductor technology comprising an illumination unit (67), an imaging optical unit (59) and a recording device (52) for imaging and capturing the object (58), characterized in that for imaging the pupil illumination of the pupil plane (66) of the imaging optical unit (59), a Bertrand module (70, 71 , 72, 74) is arranged in a free space in the imaging optical unit (59).

2. The apparatus (51 ) as claimed in claim 1 , characterized in that the Bertrand module (70, 71 , 72, 74) is arranged in such a way that at least one optical element (M1 , M2, M3, M4) of the imaging optical unit (59) is at least partly shaded by the Bertrand module (70, 71 , 72, 74).

3. The apparatus (51) as claimed in either of claims 1 and 2, characterized in that the Bertrand module (70, 71 , 72, 74) is arranged in such a way that the pupil plane (66) of the imaging optical unit (59) is imaged at least onto a part of the recording device (52).

4. The apparatus (51) as claimed in either of claims 1 and 2, characterized in that the Bertrand module (70, 71 , 72, 74) is arranged in such a way that the pupil plane (66) is imaged onto an additional recording device (73,75).

5. The apparatus (51 ) as claimed in any of the preceding claims, characterized in that the Bertrand module (70, 71 , 72, 74) comprises at least one optical Bertrand element (70.1 , 71 .1 , 71 .2, 72.1 , 74.1 ).

6. The apparatus (51) as claimed in any of claims 1 to 4, characterized in that the Bertrand module (71) comprises two optical Bertrand elements (71.1 ,71.2).

7. The apparatus (51 ) as claimed in claim 5 or 6, characterized in that the Bertrand element is embodied as an EUV mirror (70.1 , 71 .1 , 71.2, 72.1 ,74.1 ).

8. The apparatus (51 ) as claimed in any of the preceding claims, characterized in that the Bertrand module (70, 71 , 72, 74) comprises at least one mirror (M1 , M2, M3, M4) of the imaging optical unit (59) for imaging the pupil illumination of the imaging optical unit (59).

9. The apparatus (51 ) as claimed in any of the preceding claims, characterized in that the apparatus (51 ) comprises a device (1 ) for introducing a Bertrand element (70, 71 , 72, 74) into a beam path of the apparatus (51 ) for inspecting an object (58) pertaining to EUV semiconductor technology.

10. The apparatus (51) as claimed in claim 9, characterized in that the device (1 ) comprises the following features- a pivoting arm (5, 5.1 , 5.2) and the Bertrand element (70.1 , 71.1 , 71.2, 72.1 ,74.1 ) arranged on the pivoting arm, and- at least one rotary joint (10.1 , 10.2), by way of which the pivoting arm (5, 5.1 ,5.2) is pivotably mounted in the device (1 ), wherein at least one rotary joint is in the form of a flexure (10.1 , 10.2).

11. The apparatus (51 ) as claimed in claim 10, characterized in that an angle of rotation (a) of the rotary joint (10.1 , 10.2) during the pivoting-in is at least 27°, preferably at least 28°, particularly preferably at least 30°.

12. The apparatus (51 ) as claimed in either of claims 10 and 11 , characterized in that the flexure (10.1 , 10.2) has at least two elastic subregions (19.11 ).

13. The apparatus (51) as claimed in claim 12, characterized in that the at least two elastic subregions (19.11) are connected via flexurally rigid connecting elements (20.1 , 20.2).

14. The apparatus (51 ) as claimed in either of claims 12 and 13, characterized in that the summed length of the elastic subregions (19.11 ) is at least 450 mm, preferably at least 460 mm and particularly preferably at least 480 mm.

15. The apparatus (51 ) as claimed in any of claims 9 to 14, characterized in that the center of gravity (21 ) of the pivoting arm (5, 5.1 , 5.2) of the device (1 ) lies on the axis of rotation (7) of the at least one rotary joint (10.1 , 10.2).

16. The apparatus (51 ) as claimed in any of claims 9 to 15, characterized in that the pivoting arm (5, 5.1 , 5.2) comprises interchangeable balancing weights (22) for displacing the center of gravity (21 ) of the pivoting arm (5, 5.1 , 5.2) after the device (1 ) has been mounted.

17. The apparatus (51 ) as claimed in any of claims 9 to 16, characterized in that the device (1 ) has a fixing device (25) of the pivoting arm (5, 5.1 , 5.2) in a measurement position (5.2) of the pivoting arm (5).

18. The apparatus (51) as claimed in claim 17, characterized in thatthe fixing device (25) comprises a magnet, in particular an electromagnet.

19. The apparatus (51 ) as claimed in claim 18, characterized in that the pivoting arm (5, 5.1 , 5.2) comprises an anchor plate (27) for fixing the pivoting arm (5, 5.1 , 5.2) with the magnet.

20. The apparatus (51 ) as claimed in any of claims 9 to 19, characterized in that the device (1 ) has an actuator (23) for deflecting the pivoting arm (5, 5.1 , 5.2).

21. The apparatus (51 ) as claimed in claim 20, characterized in that a force transmission element (15) of the actuator (23) with the rotary joint (10.1 , 10.2) is designed in such a way that the actuator (23) can transmit only tensile forces to the pivoting arm (5, 5.1 , 5.2).

22. The apparatus (51 ) as claimed in any of claims 9 to 21 , characterized in that the at least one rotary joint (10.1 , 10.2) in a measurement position of the pivoting arm (5.1 ) is arranged in such a way that it has no or virtually no deflection from its force-free zero deflection.

23. The apparatus (51 ) as claimed in any of claims 9 to 22, characterized in that the device (1 ) comprises two rotary joints (10.1 , 10.2) in mirror-inverted form with a common axis of rotation (7).

24. The apparatus (51 ) as claimed in claim 23, characterized in that the distance between the two rotary joints (10.1 , 10.2) arranged in mirror-inverted fashion is at least 43 mm, preferably at least 45 mm, particularly preferably at least 50 mm.

25. The apparatus (51 ) as claimed in any of the preceding claims, characterized in thatthe apparatus is embodied as a mask inspection apparatus (51 ), as a mask repair apparatus, as a microscope, as a projection exposure apparatus or as a wafer inspection apparatus.

Images