Semiconductor lithography projection exposure apparatus having an optical element with a sensor reference and method for aligning a sensor reference

Abstract

The invention relates to a method for aligning a sensor reference (40) with a reference surface (31) of a subject (30) in an EUV projection exposure apparatus (1), wherein the sensor reference (40) comprises a reference element (41, 41') and a receiving element (42), wherein the receiving element (42) is arranged on the subject (30) or is implemented as part of the subject (30), the method comprising the following steps: - determining the orientation of the reference surface (31) in a reference coordinate system (32) of the subject (30), - determining the deviation of the orientation of the reference surface (31) from its intended orientation, - aligning the reference element (41, 41') with the reference surface (31) of the subject (30), ') is placed in the receiving element (42), -determines the position and orientation of the reference element (41, 41') in the reference coordinate system (32) of the body (30), -determines the deviation of the reference element (41, 41') from the intended orientation taking into account the previously determined orientation of the reference element (41, 41') and the deviation of the reference surface (31) from its intended orientation, -aligns the reference element (41, 41') with the determined intended orientation, -fixes the reference element (41, 41') in the intended orientation, and -verifies the intended orientation of the reference element (41, 41') in the reference coordinate system (32). The invention also relates to a projection exposure system (1) for semiconductor lithography, comprising an optical element (18, 19, 20), the optical element (18, 19, 20) having a body (30) which in turn comprises a receiving element (42) of a plurality of reference elements (41, 41') of a sensor reference (40) for determining the position and orientation of the optical element (18, 19, 20). The optical element (18, 19, 20) further comprises a reference surface (31) designed as an optically active surface, the orientation of the reference element (41) being aligned with the orientation of the reference surface (31), and the reference element (41) being arranged at an angular displacement of less than 100 μrad relative to the reference surface (31).

Description

[0001] This patent application claims the priority of German patent application DE 10 2019 203 838.7, the contents of which are incorporated herein in their entirety by reference.

[0002] The invention relates to a projection exposure apparatus for semiconductor lithography having an optical element with a sensor reference, and to a method for aligning a sensor reference relative to the optical element.

[0003] In projection exposure apparatuses in semiconductor lithography, the position and orientation of optical elements are crucial for the quality of the imaging of lithography masks (e.g. phase masks, so-called reticles) onto semiconductor substrates (i.e. so-called wafers) performed by the system. In order to determine the position and orientation of optical elements (in particular implemented as mirrors in EUV projection exposure apparatuses), sensor systems with six degrees of freedom are used. The sensor systems are implemented, for example, as linear encoders, which are distinguished by a high resolution and at the same time a very large measuring range. The linear encoders comprise a fixed part and a moving part, wherein the working distance (i.e. the distance between the moving part and the fixed part) is typically in the range of a few millimeters. The fixed part of the sensor is fixed to a separately mounted sensor frame, while the moving part of the sensor is arranged on the mirror. To date, projection optical units in previous EUV projection exposure apparatuses have been characterized by a folded, very compact design. This greatly simplifies the embodiment of a compact and therefore robust sensor frame. Recent design variants of projection optical units are distinguished in particular by a plurality of mirrors, which are actually arranged side by side and overall occupy a considerable amount of structural space, which greatly hinders the embodiment of a compact and robust sensor frame. One possible solution consists in determining the position and orientation of the mirror using an interferometer, which likewise has a high resolution and a large measuring range, but the working distance can be in the range of a few centimeters or more. As a result, the fixedly arranged interferometer can be arranged on one or more compact and robust sensor frames, in which case a comparatively lighter and smaller reference mirror can be fitted to the optical element. Due to very stringent requirements placed on the accuracy of the position and orientation of the mirror in the range of a few picometers [pm] or tens of microrads [μrad], in particular the requirements on the accuracy of the alignment of the orientation of the reference mirror relative to the relevant optically active surface of the optical element are in the range of 10–200 μrad. The very small tolerance of the total tilt of the sensor reference relative to the interferometer includes the mounting tolerance, the tilt of the sensor reference relative to the interferometer caused by the movement of the mirror during operation, and the tilt of the sensor reference in one of the other five degrees of freedom that is therefore not measured, as well as the drift part.

[0004] In order to align the angular orientation of the sensor reference relative to a reference surface, i.e., for example, the optically active surface of an optical element (the surface on which the light used during operation of the device usually impinges), methods are known from the literature with an adhesive gap between the reflective reference component and the receiving element, wherein the angle between the reference component and the receiving element is set by an adhesive layer of uneven thickness between the reference component and the receiving element. This has the disadvantage that the adhesive gap itself can lead to a drift of the angle due to expansion or contraction of the adhesive during curing and / or over time. This effect is additionally reinforced by adhesive gaps of different thickness and the different drift amplitudes associated therewith.

[0005] An object of the present invention is to provide a device that meets the above requirements and solves the drawbacks of the prior art.Another object of the present invention is to specify a method for aligning a sensor reference relative to a reference plane of an optical element.

[0006] This object is achieved by a device and a method having the features of the independent claims. The dependent claims relate to advantageous developments and variants of the invention.

[0007] A method according to the invention for aligning a sensor reference relative to a reference plane of a subject in an EUV projection exposure apparatus, wherein the sensor reference comprises a reference element and a receiving element, wherein the receiving element is fixedly arranged on the subject or is embodied as part of the subject, comprises the following steps:

[0008] - determine the orientation of the reference surface in the reference coordinate system of the subject,

[0009] - determine the deviation of the orientation of the reference surface from its target orientation,

[0010] - insert the reference element into the receiving element,

[0011] - determining the position and orientation of the reference element in the reference coordinate system of the subject,

[0012] - determining a deviation of the reference element from the target orientation taking into account a previously determined orientation of the reference element and a deviation of the reference surface from its target orientation,

[0013] - aligning the reference element with the determined target orientation,

[0014] - fixing the orientation of the reference element relative to the reference surface in a target orientation,

[0015] - Verify the target orientation of the reference element in the reference coordinate system.

[0016] In this case, the determination of the orientation of the reference surface in the reference coordinate system can be achieved, for example, by interferometry. For this purpose, it can be implemented that, for example, an optical element, in particular a body as a mirror of an EUV projection exposure apparatus, is positioned in a measuring machine which can determine, by interferometry, the deviation of the reference surface relative to a reference coordinate system, which is defined, for example, by reference points on the body. Due to manufacturing tolerances, the reference surface almost always has deviations from its target position and orientation, which can be determined in the manner described.

[0017] Furthermore, the receiving element can comprise a contact surface which is embodied as a conical seat.

[0018] Furthermore, the reference element can include a contact surface that is implemented as a spherical surface. The spheroconical pairing between the receiving element and the reference element results in a typically circular contact line, which enables a clear and stable orientation of the reference element in the receiving element. The direct mechanical contact thus provided between the two components can advantageously minimize drift between the reference element and the receiving element.

[0019] For accurate positioning, the reference element can be held by a mount when inserted into the receiving element. This is not critical for the first insertion, but can greatly simplify the setting of the reference element to the target position and orientation.

[0020] In particular, the mounting can have at least one actuator for tilting the mounting relative to the receiving element. This makes it possible to set the angle of the reference surface relative to the angle of the reference surface in the receiving element with very high resolution.

[0021] In a variant of the method, the weight of the reference element can be at least partially compensated by the mounting, whereby, for example, the receptacle can also be arranged head-on or sideways. Overall, the normal force can be set in a controlled manner and lateral force components (such as gravity in the case of lateral mounting) can be compensated. A further advantage of weight compensation is that the normal force at the contact line can be minimized and thus the friction between the two components can be advantageously reduced.

[0022] In other embodiments of the invention, the orientation of the reference element can be determined by the orientation of a surface of the reference element. The surface can advantageously be the reference surface of the reference element itself. However, a surface with a known alignment relative to the reference surface can also be used.

[0023] In a variant of the invention, the orientation of the reference element can be determined by the orientation of an auxiliary surface. The auxiliary surface can be implemented on an additional component, an auxiliary element, which can be arranged fixedly in position and orientation relative to the reference element and has a larger surface area than the reference surface itself. This can be advantageous, for example, because the reference reflector can be very small due to structural space restrictions and the angle determined by the detection method can be determined more simply or accurately, which can greatly limit the basis for the angle measurement by detecting a plurality of points.

[0024] In a further exemplary embodiment of the invention, the orientation of the reference element relative to a reference coordinate system can be determined by a coordinate measuring machine. An advantage of a coordinate measuring machine is that it is possible to measure large bodies in six degrees of freedom with high accuracy relative to one another in the μm range. The coordinate measuring machine can be flexibly set up for different bodies, which can have a positive impact on the process and thus on the manufacturing costs. This involves first determining the orientation of the body and thereby determining the reference coordinate system on the coordinate measuring machine. Subsequently, the orientation of the reference element relative to the reference coordinate system is determined. The deviation of the reference element from its target orientation can be determined by the deviation of the reference surface from its target orientation and the orientation of the reference surface in the reference coordinate system.

[0025] In a variant of the invention, the orientation of the reference element in the reference coordinate system can be determined by an optical measuring system. In this case, a camera can record the geometry of the reference element, which is optionally equipped with markings, and the position and orientation of the reference element can subsequently be determined by means of image evaluation. The setup is simpler and the number of moving parts is reduced by using a so-called time-of-flight camera. In addition, the measurement can be carried out more quickly than by measurement by a coordinate measuring machine, since multiple points can be captured and determined by a single recording. Once the orientation and position of the reference surface and the deviation of the position and orientation of the reference element in the reference coordinate system of the subject have been determined, the deviation of the reference element from the target orientation can be calculated therefrom in a simple manner. The position, i.e. the values ​​on the X, Y and Z axes of the reference coordinate system, is less important, since errors in the measuring direction represent only offsets and displacements perpendicular to the measuring direction can be compensated by an extension of the measuring area. Any deviation in orientation (ie tilt about the X, Y and Z axes) leads to errors in the measurement of the distance and is particularly important for large measurement distances, whose values ​​are in the range of 500-300 μrad, in particular in the range of 300-100 μrad, especially in the range of 100-10 μrad.

[0026] In a variant of the invention, during alignment of the reference element, the orientation of the reference element can be determined in situ, ie during the alignment itself. This has the advantage that the adjustment or tilting of the reference element can be directly observed, so that the target orientation can be reached more quickly.

[0027] Furthermore, during alignment of the reference element, the orientation of the reference element can be determined by the optical measuring device.

[0028] In particular, the optical measuring device can be an autocollimation telescope. The latter is particularly suitable for setting the tilt angle, since the latter must be indicated directly and not calculated by transformation from a plurality of coordinates. In the case of using an auxiliary element, by means of the autocollimation telescope both the orientation of the auxiliary element (which can be implemented as a semi-transparent mirror) in the case of a first reflection and secondly the orientation of the reference element in the case of a second reflection in the same measurement can be determined. By using the autocollimation telescope, the orientation of the auxiliary element, which can be determined more accurately than the reference element, can be transferred as is to the reference element.

[0029] In particular in the case of very small reference surfaces, during the alignment of the reference element, the orientation of the reference element relative to the auxiliary surface can be determined. This is the case when the orientation of the reference surface can no longer be determined within a given tolerance range when probing the reference surface, which can be in the range of 100 mm x 100 mm, in particular in the range of 45 mm x 45 mm, in particular in the range of 20 mm x 20 mm, but can also have a rectangular geometry. As described above, in this case the auxiliary element can be arranged at a fixed distance and orientation relative to the reference element. The auxiliary element can then be measured, for example, by a coordinate measuring machine, wherein the orientation of the auxiliary element can be determined more accurately than the orientation of the reference element. During the alignment of the reference element with the desired target orientation, the orientation of the reference element relative to the auxiliary element and therefore also relative to the reference surface can then be aligned by an autocollimation telescope.

[0030] If the orientation of the reference surface corresponds to the desired target orientation, the latter can be fixed to the receiving element, for example, by adhesive bonding. To this end, the adhesive can be applied from the outside to the adhesive gap around the contact line or just above the contact line, for example, via a lateral opening or hole in the conical seat or region of the receiving element, so that uniform and complete wetting of the adhesive can be ensured at the periphery. This results in a connection with high strength and minimal drift behavior due to direct mechanical contact. It is also conceivable to check the complete wetting of the adhesive by a decompression test before curing or an additional pressure or reduced pressure test after curing. To this end, an additional pressure or a reduced pressure can be generated in the space below the contact line in the receiving element.

[0031] Furthermore, the orientation of the reference element can be verified by a coordinate measuring machine after the reference element has been fixed in a target orientation.

[0032] Furthermore, the orientation of the reference element can be checked by an optimal measuring system. Due to the alignment of the reference surface relative to the imaging quality-relevant reference surface of the subject in the reference coordinate system, the method can achieve very low orientation tolerances, which can be in the range of 500-300 μrad, in particular in the range of 300-100 μrad, in particular in the range of 100-10 μrad.

[0033] The projection exposure device for semiconductor lithography according to the present invention comprises an optical element, which comprises a main body as part thereof, the main body having a receiving element of a plurality of reference elements of a sensor reference for determining the position and orientation of the optical element. In addition, the optical element comprises a reference surface implemented as an optically effective surface, the orientation of the reference element being aligned relative to the orientation of the reference surface. In particular, the angular deviation of the reference element relative to the reference surface is less than 100 μrad. Therefore, the optical element achieves a positioning accuracy that corresponds to the requirements for the imaging quality of the EUV projection exposure device. The receiving element can be arranged and fixed on the main body as a separate component, or can be implemented as a part of the main body, that is, implemented as a whole.

[0034] In a variant of the invention, the receiving element can comprise a contact surface embodied as a conical seat.

[0035] Furthermore, the reference element can include a contact surface which is implemented as a spherical surface. The spheroconical pairing reduces the contact of the two contact surfaces to a circular contact line, which results in a drift-stable mechanical contact between the two components.

[0036] Furthermore, the reference element can be fixed in the receiving element by means of an adhesive.

[0037] For example, the adhesive can be applied from the outside to the entire periphery so that it can at least partially touch the contact line between the contact surfaces. Due to the application of the adhesive to the entire periphery and curing, a connection with high stiffness and at the same time high drift stability can be formed. The adhesive applied uniformly to the periphery also produces uniform tensile stresses during curing and can advantageously minimize tilting or warping of the reference element in the receiving element. Similarly, the adhesive can flow over the contact line at the cutout or extend along the contact line, resulting in complete wetting of the adhesive gap but no or obvious flow over the contact line. A variety of geometries can be envisaged for the cutouts; they can be arranged on one of the two elements to be connected, or on both elements to be connected. It is also conceivable to apply the adhesive in points.

[0038] In a variant of the invention, the contact surfaces of the reference element and / or the receiving element may be at least partially coated to reduce friction. The coating reduces the friction between the reference element and the receiving element, thereby advantageously simplifying the alignment process.

[0039] Furthermore, the receiving element can be arranged in the space bounded by the cutout in the receiving element and the spherical surface of the reference element to generate an additional pressure for reducing friction at the contact line or a reduced pressure for monitoring the quality of the connection. Likewise, at least one reference element can include an observation window for this purpose.

[0040] Furthermore, alignment of the reference element with the target orientation may be achieved by changing the geometry of the reference element or the receiving element; alternatively or additionally, this may also be achieved by adjusting the thickness of the bonding gap.

[0041] Exemplary embodiments and variants of the present invention are explained in more detail below with reference to the accompanying drawings, in which:

[0042] Figure 1 shows the basic setup of an EUV projection exposure tool,

[0043] Figure 2 shows a schematic detail diagram of the present invention,

[0044] Figure 3a Showing other schematic details of the present invention,

[0045] Figure 3b Showing other schematic details of the present invention,

[0046] Figure 4 Showing other schematic details of the present invention,

[0047] Figure 5a , b shows other schematic details of the present invention,

[0048] Figure 6 Showing other schematic details of the present invention,

[0049] Figure 7a , b each show a schematic diagram of a measuring component,

[0050] Figure 8a , b shows a variation of the present invention,

[0051] Figure 9a , b shows other variations of the present invention, and

[0052] Fig.10 A flow chart showing a manufacturing method according to the present invention is shown.

[0053] Figure 1An example of a basic setup of a microlithography EUV projection exposure apparatus 1 in which the invention can be used is shown. The illumination system of the projection exposure apparatus 1 has, in addition to the light source 3, an illumination optical unit 4 for illuminating an object field 5 in an object plane 6. EUV radiation 14 in the form of optically usable radiation generated by the light source 3 is collimated by a collector, which is integrated in the light source 3, so that the radiation passes through an intermediate focus in the region of an intermediate focal plane 15 and is then incident on the field facet mirror 2. Downstream of the field facet mirror 2, the EUV radiation 14 is reflected by a pupil facet mirror 16. By means of the pupil facet mirror 16 and an optical assembly 17 with mirrors 18, 19 and 20, the field facets of the field facet mirror 2 are imaged into the object field 5.

[0054] A reticle 7 is illuminated, which is arranged in the object field 5 and is held by a schematically illustrated reticle holder 8. A projection optical unit 9, which is only schematically illustrated, serves to image the object field 5 into an image field 10 in an image plane 11. The structures on the reticle 7 are imaged onto a photosensitive layer of a wafer 12, which is arranged in the region of the image field 10 in the image plane 11 and is held by a likewise partially illustrated wafer holder 13. The light source 3 can emit the radiation used, in particular in a wavelength range between 5 nm and 30 nm.

[0055] Figure 2 A body 30 is shown, which can be embodied as an optical element 30, in particular in the manner of mirrors 18, 19, 20 of an EUV projection exposure device 1. The body 30 comprises a reference surface 31 embodied as a concave surface. A z-axis 33 of a reference coordinate system 32 is illustrated as being perpendicular to the concave reference surface 31, said z-axis being embodied as an optical axis 33 and extending perpendicularly to the reference surface 31 and passing through its vertex 34. Due to manufacturing tolerances, the reference surface 31 deviates from a target reference surface 31' as indicated by a dashed line. The body 30 further comprises a receiving element 42, which together with the reference element 41 forms a sensor reference 40. The geometry of the receiving element 42 can alternatively also be embodied in the body 30 and form a component therewith. The latter can in particular be embodied as a reference mirror 40 of an interferometer. A reference coordinate system 43 is likewise assigned to the reference element 41, wherein the z-axis is perpendicular to a reference surface 44 of the reference element 41 (see Figure 3a ). The reference element 41 is aligned relative to the reference surface 31 so that the orientation of the reference surface 44 compensates for deviations of the orientation of the reference surface 31 relative to the body 30, so that the reference element 41 is perpendicular to the beam path of the interferometer in the zero position (i.e. in the position in which the body 30 is optimally aligned in the projection optical unit). Thus, parasitic errors caused by the tilt of the reference element 41 relative to the interferometer beam path can be advantageously minimized. The dotted line illustrates the orientation of the reference element 41 'after insertion into the receiving element and before alignment.

[0056] Figure 3a A sensor reference 40 is shown comprising a reference element 41 and a receiving element 42. The reference element 41 comprises a contact surface 46 implemented as a spherical surface 46 on a first side and a reference surface 44 on a second side. A shoulder 48 is implemented above the spherical surface 46 and serves to allow the reference element 41 to be received in a mounting (not shown). In addition Figure 3a In addition to the shoulder 48 shown in FIG. 4 , other structures or surfaces on the reference element 41 are also conceivable to allow receiving the reference element 41 in a mounting (not shown). The receiving element 42 comprises a cutout 50, at the upper end of which a contact surface 47 is implemented as a conical surface 47. Furthermore, the receiving element 42 comprises a hole 49 perpendicular to the cutout 50, which ventilates the space 51 generated by the placement of the spherical surface 46 of the reference element 41 on the conical surface 47 of the receiving element 42. The spherical surface 46 and the conical surface 47 contact each other at the contact line 45. In order to check the contact and later the adhesive bond 53 (which will be shown in FIG. 4 ), the contact surface 47 is formed by the spherical surface 46 of the reference element 41. Figure 3b ), the reference element 41 comprises an observation window 52 which allows the contact line 45 and the adhesive bond 53 to be inspected.

[0057] Figure 3b The fixing 53 of the reference element 41 on the receiving element 42 and the contact line 45 are shown in detail, said fixing being implemented as an adhesive bond 53. After the reference element 41 has been aligned, it is fixed by the adhesive bond 53, which is applied from the periphery over the entire periphery and touches the contact line 45. By capillary action, the adhesive 53 is pulled up to the contact line 45 and is stretched around and along the periphery of the sphere, thus producing a rigid connection between the reference element 41 and the receiving element 42. In order to check the adhesive bond 53, it can be checked by Figure 3a The illustrated holes 49 create a reduced pressure in the space 51 below the spherical surface 46 .

[0058] Figure 4 A mounting member 60 for a reference element 41 (not shown) is shown, the mounting member being used to align the reference element 41 with the receiving element 42 and comprising a receptacle 62. The reference element 41 is aligned with the receiving element 42 by Figure 3a The shoulder 48 shown in FIG. is inserted into the receiver 62 of the mounting member 60. Figure 3aAs further described, further alternatives are also conceivable which allow receiving the reference element 41 in the mounting 60. The mounting 60 comprises two actuators 61, 61' which are arranged to allow tilting of the reference element 41 about two mutually orthogonal axes about a center point of the spherical surface 46 of the reference element 41, said center point coinciding with the pivot point 66 of the mounting. It is also conceivable to have a mounting 60 in which the pivot point 66 of the mounting 60 and the center point of the spherical surface 46 do not coincide. The axis of rotation 65 of the first actuator 61 thus extends through the axis of the second actuator 61' and vice versa, wherein the axes of rotation 65, 65' are perpendicular to each other. One side of the mounting 60 can be embodied as a solid body with a feed element or, alternatively as shown, as a spring 63 which, by means of a spring contact surface 64, fixes the reference element 41 in the mounting 60 and prevents sliding relative to the receiving element 42 during alignment. In an alternative, the spring 63 can be moved in the effective direction of the spring 63 , for example by a threaded connection, whereby different reference elements 41 can be held by one mounting 60 , or the force of the spring 63 can be adjusted.

[0059] Figure 5a A schematic arrangement of an autocollimating telescope 70, designated hereinafter as ACT 70, an auxiliary element 75 including an auxiliary surface 78, and a sensor reference 40 is shown. The ACT 70 determines the tilt of an object relative to the optical axis of the ACT 70, wherein a collimated light beam 71 impinges on the object, which reflects the light beam 71, which is then focused on a detector (not shown in the figure). The tilt of the object results in a migration of the reflection point on the detector. From the distance between the two points or the distance between the reflections 72, 72' on the detector and the zero point of the ACT 70, i.e. the point on the detector indicating that the object is not tilted relative to the ACT 70, an angle can be determined. The auxiliary element 75 is implemented as a partially transmitting mirror or a glass plate, so that part of the light beam 71 is reflected at the auxiliary surface 78 and detected by the detector in the ACT 70, and part of the light beam 71 impinges on the reference element 41, which likewise reflects the light beam 71 and generates another point on the detector. By means of the auxiliary element whose angular orientation can be well determined by a coordinate measuring machine due to its relatively large area, the orientation of sensor reference 40 can be reliably and accurately derived from the relative orientation of two points relative to each other or to a zero point.

[0060] Figure 5bA display 74 of an ACT 70 is shown on which a coordinate system with a zero point and two crosshairs 73, 73' is represented. The crosshairs 73 represented by a solid line define the angle of the auxiliary element 75, while the crosshairs 73' represented by a dashed line define the angle of the reference element 41 relative to the ACT 70. During the alignment of the reference element 41, the determined deviation from the target orientation is set relative to the measured auxiliary element 75. First, the reference element 41 is set so that the two crosshairs 73, 73' overlap and starting from this orientation, the deviation from the target orientation is set. It is also possible to directly set the target orientation of the reference element 41 without previously aligning the reference element parallel to the auxiliary element 75.

[0061] Figure 6 A coordinate measuring machine 80 is shown, which is designated as CMM 80 in the following, and a robot 83 arranged next to the CMM 80, to whose arm 84 an ACT 70 is fixed. Arranged on the CMM 80 is a receptacle 81 with a fixture 82, which is configured to receive and fix a body 30 on which a sensor reference element 40 is arranged. Furthermore, the receptacle 81 can also be mounted on a rotation table (not shown), thereby also expanding the possibilities for aligning the body 30 relative to the ACT 70. The CMM 80 first determines the orientation of the body 30 by probing reference points and thereby a reference coordinate system 32 (not shown) of the body 30, and then determines the orientation of the sensor reference element 40 in the reference coordinate system 32 of the body 30 by probing reference surfaces 44. If the deviation of the sensor reference element 40 has been determined, the ACT 70 is positioned with the aid of the robot 83 to measure the angle of the reference element 41, as Figure 5a and 5b The ACT 70 determines the angle of the reference surface 44 in situ, that is to say continuously, so that the relative alignment of the reference surface 44 can be observed at the ACT 70. After aligning the reference element 41, the latter is fixed and can eventually be oriented again by the CMM 80 for monitoring purposes.

[0062] Figure 7aAn alternative arrangement for aligning a reference element 41, 41' with an optical measuring system 85, 85' implemented as a camera 85, 85' is shown, the number and the capture range of the cameras 85, 85' being shown only schematically. As an example, the measuring system may comprise 3 cameras, whereby a 3-point reference to the markers is possible, or a so-called time-of-flight camera may be used, which can determine distances by the time-of-flight method. The positions of the cameras 85, 85' of the measuring system 85, 85' are known in space and relative to each other. With the aid of markers 86 adapted on the body 30, whose positions in the reference coordinate system 32 of the body 30 are known, the measuring system 85 determines the position and orientation of the reference coordinate system 32 of the body 30, and then the position and orientation of the sensor reference 40 in the reference coordinate system 32 can be determined by one or more images. The ACT 70 fixed to the arm 84 of the robot 83 is likewise used for aligning the reference surface 44 of the sensor reference 40. The position and orientation of the ACT 70 are determined by the markers 86' captured by the second camera 85' of the measuring system 85, 85'. The body 30 is arranged on an adjustment stage 87. Due to the use of the adjustment stage 87, it is also possible to use a fixedly mounted ACT 70, since the reference surface 44 can be aligned relative to the ACT 70 by means of the adjustment stage.

[0063] Figure 7b A further alternative arrangement for aligning the reference elements 41, 41' in a measuring frame 88 comprising a fixedly mounted camera 85 and an interferometer 89 is shown. The system can be calibrated by means of a so-called gold body, i.e. a reference body, wherein the interferometer 89 is aligned relative to the gold sensor reference 40. For aligning the reference elements 41, 41' (not shown) of the sensor reference 40, the body 30 is fixed on an adjustment stage 87 which can be adjusted in up to six degrees of freedom. The position and orientation of the body 30 are set so that it corresponds to the position and orientation of the gold body 30 in the measuring frame 88. The reference element 41 can then be aligned by means of the calibrated interferometer 89 taking into account the deviation of the reference surface 31 from the target reference surface 31' (specific to the body 30). If, for example, the deviation of the reference surface 31 is equal to zero, the reference element is aligned with the position and orientation of the reference element of the gold sensor reference. An advantage of the measuring arrangement is that the orientation of the reference element 41 does not have to be predetermined by means of a detection or optical measuring device, since the target position of the reference element 41 can be set in absolute terms by the interferometer 89 calibrated with the gold body. In order to align the reference elements 41 of the sensor reference 40 relative to the fixedly mounted interferometer 89, the bodies 30 can likewise be aligned correspondingly with the adjustment stage 87, wherein the position and orientation of the bodies 30 again correspond to the position and orientation of the gold bodies of the respective reference elements 41. Alternatively, for each sensor reference 40, an ACT 70 (not shown) can be arranged in the measurement frame 88 and they can be calibrated with the gold bodies with the gold sensor reference as described above.

[0064] Figure 8a and 8b Other alternatives for aligning the orientation of the reference element 41 of the sensor reference 40 relative to the orientation of the reference surface 31 of the body 30 are shown. After determining the deviation of the orientation of the nominal reference element 90 from its target orientation, as Figure 8a As shown, the reference element 90 is re-machined according to the determined deviation and connected to the receiving element 42 again to update the inspection orientation. If the orientation of the adapted reference element 90' is within the tolerance range of the target orientation, the reference element 90' is permanently fixed in the receiving element 42. Alternatively or additionally, as Figure 8b As shown, the contact surface 91' in the receiving element 94 may be re-machined to align the orientation of the reference element 41 with the target orientation. Figure 8a The nominal geometry of the reference element 90 and Figure 8b The nominal geometry of the receiving element 91 in FIG. 3 is shown in each case by dashed lines. The body 30 and the receiving element 94 can alternatively be implemented in an integral manner. It is also conceivable to process the reference element 90 ′ based on the calculated deviation and to connect it directly to the receiving element 94.

[0065] Figure 9a and 9b Two alternatives known from the prior art are shown, in which the orientation of the reference element 41 of the sensor reference 40 is set by the thickness of the adhesive gap 92, 92'. In this case, the receiving element 94 comprises three contact points 95 in order to ensure a statically determined orientation of the reference element 41. Figure 9a In the embodiment shown in FIG. 1 , the target orientation of reference element 41 of sensor-reference part 40 is set exclusively by the thickness of adhesive gaps 92 , 92 ′ at three support points 95 .

[0066] Figure 9b Shows Figure 9a , in which the adhesive gaps 92 and 92' at all contact points 95 are configured to be identical and as small as possible. The different distances required between the reference element 41 and the contact points 95 of the receiving element 94 for aligning the orientation of the reference element 41 are achieved by spacer elements 93, 93' of different heights, so-called spacer elements 93, 93'. This has the advantage that a small adhesive thickness enables drift to be reduced to a minimum.

[0067] Fig.10 A method according to the invention for aligning a sensor reference relative to a reference plane of a subject in an EUV projection exposure tool is described, wherein the sensor reference comprises a reference element and a receiving element, wherein the receiving element is arranged on the subject or is embodied as part of the subject.

[0068] A first method step 100 involves determining the orientation of a reference surface in a reference coordinate system of the subject.

[0069] The second method step 101 involves determining the deviation of the orientation of the reference surface from its target orientation.

[0070] The third method step 102 involves inserting the reference element into the receiving element.

[0071] A fourth method step 103 involves determining the position and orientation of the reference element in the reference coordinate system of the subject.

[0072] A fifth method step 104 involves determining the deviation of the determined orientation from the target orientation of the reference element taking into account the previously determined orientation of the reference element and the deviation of the reference surface from its target orientation.

[0073] A sixth method step 105 involves aligning the reference element with the determined target orientation.

[0074] A seventh method step 106 involves fixing the reference element in the target orientation.

[0075] An eighth method step 107 involves checking the target orientation of the reference element in the reference coordinate system.

[0076] By means of this method, a sensor reference in the range of 500–300 μrad, in particular in the range of 300–100 μrad, in particular in the range of 100–10 μrad can be achieved, which has a favorable effect on the accuracy of the orientation control of the optical elements in the device.

[0077] Reference numerals list

[0078] 1 Projection exposure equipment

[0079] 2 Faceted Mirrors

[0080] 3 Light Source

[0081] 4 Illumination optical unit

[0082] 5. Material Field

[0083] 6 Object Plane

[0084] 7. Mask Master

[0085] 8 Mask master holder

[0086] 9 Projection optics unit

[0087] 10 Image Field

[0088] 11 Image plane

[0089] 12 chips

[0090] 13 Wafer holder

[0091] 14 EUV Radiation

[0092] 15 Intermediate field focal plane

[0093] 16-Pupil Faceted Mirror

[0094] 17 Assembling parts

[0095] 18 Reflector

[0096] 19 Reflector

[0097] 20 Reflector

[0098] 30 Main Body

[0099] 31,31' Reference surface

[0100] 32 Reference coordinate system

[0101] 33 Optical axis

[0102] 34 Vertex

[0103] 40 Sensor reference

[0104] 41,41' Reference element

[0105] 42 Receiving element

[0106] 43 Reference element coordinate system

[0107] 44 Reference surface

[0108] 45 Contact Line

[0109] 46 Contact surface of reference element

[0110] 47 Contact surface of receiving element

[0111] 48 Shoulder

[0112] 49 holes

[0113] 50 Cut

[0114] 51 Extra Pressure Space

[0115] 52 Observation Window

[0116] 53 Adhesive

[0117] 60 Mounting parts

[0118] 61,61' Actuator

[0119] 62 Receiver

[0120] 63 Spring

[0121] 64 Spring contact surface

[0122] 65,65' Rotation axis

[0123] 66 Pivot point of mounting

[0124] 70 Optical measuring devices, autocollimating telescopes

[0125] 71 Beam

[0126] 72,72' Reflection

[0127] 73,73' Crosshairs

[0128] 74 Display

[0129] 75 Auxiliary components

[0130] 76 Coordinate system

[0131] 77 Zero

[0132] 78 Auxiliary Surface

[0133] 79 CMM measuring head

[0134] 80 Coordinate Measuring Machine

[0135] 81 Coordinate measuring machine receiver

[0136] 82 CMM Fixing Parts

[0137] 83 Robot

[0138] 84 Robot Arm

[0139] 85,85' Camera

[0140] 86,86' mark

[0141] 87 Adjustment table

[0142] 88 Measurement Frame

[0143] 89 Interferometer

[0144] 90,90' Reference element (individualized)

[0145] 91,91' Contact surface of receiving element (individualized)

[0146] 92,92' Adhesive Gap

[0147] 93,93' Spacer

[0148] 94 Receiving element

[0149] 95 contact point; bonding surface

[0150] 100 Method Step 1

[0151] 101 Method Step 2

[0152] 102 Method Step 3

[0153] 103 Method Step 4

[0154] 104 Method Step 5

[0155] 105 Method Step 6

[0156] 106 Method Step 7

[0157] 107 Method Step 8

Claims

1. A method for aligning a sensor reference (40) relative to a reference surface (31) of a body (30) in an EUV projection exposure apparatus (1), wherein the sensor reference (40) comprises a reference element (41, 41') and a receiving element (42), wherein the receiving element (42) is fixedly arranged on the body (30) or is embodied as part of the body (30), the method comprising the following steps: - determining the orientation of the reference surface (31) in a reference coordinate system (32) of the body (30), - determining the deviation of the orientation of the reference surface (31) from its target orientation (31'), - after determining the deviation of the reference surface, inserting the reference element (41, 41') into the receiving element (42), - determining the position and orientation of the reference element (41, 41') in a reference coordinate system (32) of the body (30), - determining the deviation of the reference element (41, 41') from the target orientation taking into account the previously determined orientation of the reference element (41, 41') and the deviation of the reference surface (31) from its target orientation (31'), - aligning the reference element (41, 41') with the determined target orientation, - fixing the orientation of the reference element (41, 41') relative to the reference surface (31) at the target orientation, - checking the target orientation of the reference element (41, 41') in the reference coordinate system (32), Therein, the reference surface is configured such that during use of the EUV projection exposure apparatus, the reference surface reflects EUV radiation.

2. The method according to claim 1, It is characterized in that The orientation of the reference surface (31) in the reference coordinate system (32) is determined by interferometry.

3. The method according to claim 1 or 2, It is characterized in that The receiving element (42) comprises a contact surface (47) which is embodied as a conical seat (47).

4. The method according to any one of the preceding claims, It is characterized in that The reference element (41, 41') comprises a contact surface (46) embodied as a spherical surface (46).

5. The method according to any one of the preceding claims, It is characterized in that The reference element (41, 41') is held by a mount (60) when inserted into the receiving element (42).

6. The method according to claim 5, It is characterized in that The mounting element (60) has at least one actuator (61, 61') for tilting the mounting element (60) relative to the receiving element (42).

7. The method according to claim 5 or 6, It is characterized in that The weight of the reference element (41, 41') is at least partially compensated by the mounting (60).

8. The method according to any one of the preceding claims, It is characterized in that The orientation of the reference element (41, 41') is determined by the orientation of the surface (44) of the reference element (41, 41').

9. The method according to any one of claims 1 to 7, It is characterized in that The orientation of the reference element (41, 41') is determined by the orientation of the auxiliary surface (78).

10. The method according to any one of the preceding claims, It is characterized in that The orientation of the reference element (41, 41') relative to the reference coordinate system (32) is determined by a coordinate measuring machine (80).

11. The method according to any one of claims 1 to 9, It is characterized in that The orientation of the reference element (41, 41') relative to the reference coordinate system (32) is determined by an optical measuring system (85, 85').

12. The method according to any one of the preceding claims, It is characterized in that During alignment of the reference element (41, 41'), the orientation of the reference element (41, 41') is determined in situ.

13. The method according to any one of the preceding claims, It is characterized in that During alignment of the reference element (41, 41'), the orientation of the reference element (41, 41') is determined by an optical measuring device (70).

14. The method according to claim 13, It is characterized in that The optical measuring device (70) is a self-collimating telescope (70).

15. The method according to any one of the preceding claims, It is characterized in that The target orientation of the reference element (41, 41') is fixed by adhesive bonding to the receiving element (42).

16. The method according to any one of the preceding claims, It is characterized in that The target orientation of the reference element (41, 41') is checked by a coordinate measuring machine (80).

17. The method according to any one of the preceding claims, It is characterized in that The target orientation of the reference element (41, 41') is checked by an optical measuring system (85, 85').

18. The method according to any one of the preceding claims, It is characterized in that The reference element (41, 41') is aligned with the target orientation by a change in the geometry of the reference element (40, 41) or the receiving element.

19. The method according to any one of the preceding claims, It is characterized in that Alignment of the reference element (41, 41') with the target orientation is achieved by adapting the thickness of the adhesive gap (92, 92').

20. A projection exposure apparatus (1) for semiconductor lithography, the projection exposure apparatus (1) comprising: - an optical element (18, 19, 20) comprising: - a body (30) comprising receiving elements (42) of a plurality of reference elements (41, 41') of a sensor reference (40) for determining the position and orientation of said optical elements (18, 19, 20), a reference surface (31) embodied as an optically active surface, the orientation of the reference element (41) being aligned relative to the orientation of the reference surface (31), It is characterized in that The method according to claim 1 is performed using the projection exposure apparatus such that the reference element (41) is arranged with an angular deviation of less than 100 μrad relative to the reference surface (31), Therein, the reference surface is configured such that during use of the EUV projection exposure apparatus, the reference surface reflects EUV radiation.

21. The projection exposure apparatus (1) according to claim 20, It is characterized in that The reference element (42) comprises a contact surface (47) which is embodied as a conical seat (47).

22. The projection exposure apparatus (1) according to claim 20 or 21, It is characterized in that The reference element (41) comprises a contact surface (46) which is embodied as a spherical surface (46).

23. The projection exposure apparatus (1) according to any one of claims 20 to 22, It is characterized in that The reference element (41) is fixed in the receiving element (42) by means of an adhesive (53).

24. The projection exposure apparatus (1) according to claim 23, It is characterized in that The adhesive (53) at least partially touches the contact line (45) between the contact surfaces (46, 47).

25. The projection exposure apparatus (1) according to any one of claims 22 to 24, It is characterized in that The contact surfaces (46, 47) of the reference element (41) and / or the receiving element (42) are at least partially coated to reduce friction.

26. The projection exposure apparatus (1) according to any one of claims 22 to 25, It is characterized in that The receiving element (42) is configured to generate, in a space (51) delimited by a cutout (50) in the receiving element (42) and a spherical surface (46) of the reference element (41), an additional pressure for reducing friction at the contact surfaces (46, 47) or a reduced pressure for testing the fixation of the reference element (41).

27. The projection exposure apparatus (1) according to any one of Claims 22 to 26, It is characterized in that At least one of the reference elements (41) comprises a viewing window (52).

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