Method for manufacturing an optical test element for determining a fit defect of an optical surface

Abstract

Method for producing an optical test element (19) for determining a fit defect of an optical surface (20). The method comprises the following steps: - Determining a CGH design (24) suitable for measuring the optical surface (20), - Generating a CGH auxiliary structure (25) corresponding to the CGH design (24) on an auxiliary substrate (30) using a direct-write lithography process, - Generating an image of the CGH auxiliary structure (25) on a final substrate (40) using a transfer lithography process, - Generating a CGH structure (50) corresponding to the CGH design (24) based on the generated image. The method offers the advantage that the auxiliary substrate can be produced with high precision using a standardized direct-write lithography system, regardless of the size of the optical test element.

Description

The invention relates to a method for producing an optical test element for determining a fit error of an optical surface.It is known in principle to use optical test elements in the form of a computer-generated hologram (CGH) for interferometric measurements in order to determine a fit error of an optical surface (WO 2005 / 114101 A1, DE 10 2015 202 695 A1, DE 10 2012 217 800 A1, DE 10 2019 204 096 A1). A part of a test beam path that impinges on the CGH, also referred to as input wave in the present case, is diffracted with the aid of the CGH in such a way that a resulting part of the test beam path, referred to as output wave for short in the following, forms a wavefront that is matched to the desired shape of the optical surface. This means that the output shaft impinges perpendicularly on the optical surface to be checked, provided that the optical surface corresponds to its desired shape and is positioned in a suitable manner. The output shaft striking the optical surface is then reflected into itself and used together with a reference beam path for generating an interference signal. The interference signal can be used to make statements about the fit of the optical element.The CGH usually comprises a transparent or reflective substrate provided with a grid-like microstructure. Different partial shafts of the input shaft meet the grid-like structure at different points and experience a phase modulation dependent on the grid structure there when transitioning into corresponding partial shafts of the output shaft. On the optical surface to be examined, the different partial waves of the output wave interfere in such a way that the wavefront arising is matched to the desired shape of the optical surface. The desired phase modulation can be described by a phase function in which the transition from the input shaft to the output shaft is described. If the phase function is present, a suitable CGH design can be determined by calculation in a known manner. The design can be transferred to a CGH substrate in a manner known in principle by methods of structurization.In order for a CGH to produce an output wave which is reflected into itself over the entire optical surface, the CGH must have a certain minimum extent in the surface perpendicular to the optical axis of the input wave, which is dependent on the size and curvature of the optical surface to be tested. The larger and the more convexly curved the optical surface, the larger must also be the dimensions of the CGH in order to be able to cover the entire optical surface. This is problematic because available methods for producing the CGH microstructures meet technical-physical limits for particularly large substrates to be structured.In order to be able to measure large optical surfaces nevertheless, it has been proposed in the prior art to arrange a plurality of separate CGHs to form a composite, such that different parts of the input shaft pass through different CGHs (cf. U.S. Pat. No. 8,941,837 B1). However, this results in a disadvantage that each of the CGHs must be adjusted with high accuracy, which is associated with a great amount of effort and the problem that the CGHs can drift relative to each other. In addition, gaps arise between the individual CGHs for which no measured values can then be determined, in particular in the case of free-form surfaces.It is the object of the present invention to at least partially avoid the above-described disadvantages. This object is achieved with the features of the independent claims. Advantageous embodiments are described in the dependent claims.Accordingly, the invention relates to a method for producing an optical test element for determining a fit error of an optical surface, comprising the following steps:determining a CGH design suitable for measuring the optical surface,creating a CGH assist pattern conforming to the CGH design on an assist substrate using a direct write lithography process,generating an image of the CGH auxiliary structure on a final substrate with the aid of a transmitting lithography method,producing a CGH structure corresponding to the CGH design on the basis of the generated image.First, some terms used in the invention will be explained. The final substrate can be a transparent substrate, in particular made of quartz glass. The CGH structure can be formed, for example, by a sequence of elevations or depressions in the substrate. It is also possible for the CGH structure to be formed by a sequence of transparent and opaque regions. In the case of a reflective CGH, the CGH structure can be formed by a sequence of structures with different reflectivities, for example by a sequence of reflective and non-reflective regions or by elevations and depressions in a reflective layer. The final substrate provided with the CGH structure forms the optical test element for determining a fit error.Direct write lithography methods are considered to be those lithography methods in which a desired structure is transferred to a substrate with the aid of a spatially greatly delimited or focused writing medium. The direct writing lithography method can be, in particular, an electron beam lithography method or a laser beam lithography method. These two methods are distinguished in that a spatially strongly focused electron beam or laser beam is used to write a structure onto the substrate (or a lacquer layer located there). It may be possible here for the writing medium (i.e. the electron beam or the laser beam) to be movable by suitable deflection means over a limited distance relative to the fixed substrate. However, in order to write large area substrates, it is necessary to move the substrate relative to the writing medium.In the present case, transfer lithography methods are considered to be methods which differ from a direct writing lithography method in that a structure previously already produced, for example, on a mask or a stamp is transferred over a large area to the final substrate. An example of a transferring lithography method is the nanoimprint lithography (also referred to as "nanoimprint lithography"), which is fundamentally known from the prior art, in which microstructures are produced on a "stamp" and are mechanically transferred into a suitable coating, which has previously been applied to a final substrate. Another example of a transferring lithography method is X-ray lithography, in which a microstructure produced on a mask is positioned at a small distance from a final substrate in order to transfer the microstructure to the final substrate by "shadow casting".In the context of the transferred lithography method, it can be provided that the image of the CGH auxiliary structure is generated on the final substrate in a suitable coating applied to the final substrate. The CGH structure can then be produced with the aid of fundamentally known methods for structurization on the basis of the image produced.It is not necessary that the CGH auxiliary structure be identical to the CGH structure to be produced. It is possible in particular for the CGH auxiliary structure to represent a "negative" of the CGH structure. This can be the case, for example, if nanoimprint lithography is selected as the transferring lithography method, in which a structure maximum on the stamp (i.e., in the present case a maximum of the CGH auxiliary structure) is usually transferred into a structure minimum of a coating located on the final substrate, wherein the structure minimum in the coating can be transferred into a structure minimum of the CGH structure by a copolymerization method.In conventional direct write lithography methods, the substrate to be written is moved relative to the write beam in order to produce the desired microstructures on the entire substrate, since only small regions of a few 100 μm can be exposed via beam deflection. In particular in the case of large-area substrates, these must be greatly accelerated and decelerated in order to keep the time required for writing the microstructures over the large area of the substrate within acceptable limits. In the case of large-area substrates, direct writing lithography methods can therefore meet mechanical limits. In the context of the method according to the invention, on the other hand, a CGH auxiliary structure can first be produced on an auxiliary substrate with the aid of a highly precise direct write lithography method, wherein the size of the auxiliary substrate can be selected independently of the size of the final substrate.According to one embodiment, it is provided that the auxiliary substrate has a lower mass than the final substrate. In this embodiment, therefore, a CGH auxiliary structure can first be produced on an auxiliary substrate, which has a smaller mass than the final substrate, with the aid of a direct write lithography method. The auxiliary substrate can be produced more easily and with higher positional accuracy because of the lower mass. Only in a subsequent step is the CGH auxiliary structure transferred to the final substrate with the aid of the transferred lithography method. It was recognized that a high positional accuracy of the microstructures produced within the auxiliary substrate can be transferred to the CGH structure of the final substrate by the transferring lithography method without significantly impairing the positional accuracy.In particular, the auxiliary substrate can have a smaller thickness than the final substrate. For example, a thickness of the auxiliary substrate may be less than or equal to 20 mm. A thickness of the final substrate can be, for example, between 30 mm and 200 mm, preferably between 50 mm and 120 mm. Furthermore, a ratio of the diameter of the final substrate to the thickness of the final substrate can be between 3:1 and 10:1, in particular between 4:1 and 6:1. A final substrate of the above-mentioned dimension is regularly suitable for imparting sufficient stability to the CGH during the later use for measuring the optical surface. At the same time, the auxiliary substrate having a thickness of 20 mm or less can be produced much more easily within the scope of a standardized direct writing lithography method available with high accuracy.In one embodiment, it is provided that the determined CGH design is divided into a number of sub-designs, wherein the auxiliary substrate has a corresponding number of sub-substrates. The number of part designs is arbitrary. The number of part designs can be, for example, between 2 and 36, in particular between 4 and 16. The number of part designs may also be at least 50 or at least 100. Furthermore, the generation of the CGH auxiliary structure can comprise a part of the CGH auxiliary structure being generated in each case on the subsubstrates using in each case one of the sub-designs. The CGH auxiliary structure is thus formed in this case from the entirety of its parts located on separate subsubstrates.By producing the CGH auxiliary structure not on one piece but on a plurality of separate subsubstrates, each individual subsubstrate has a significantly smaller diameter and a correspondingly lower weight compared to a corresponding CGH auxiliary substrate produced from one piece. It is therefore possible to produce the parts of the CGH auxiliary structure on the subsubstrates individually in each case with the aid of a standardized and very positionally accurate direct writing lithography method.It can furthermore be provided that the generation of an image of the CGH auxiliary structure takes place in that images of the parts of the CGH auxiliary structure are generated in partial regions of the final substrate. The images of the different parts can be generated in particular successively in different subareas, so that in this way the entire image of the CGH auxiliary structure is composed of the individual images of the parts. In this way, a composite CGH structure can be produced in the final substrate, which has an area that is many times larger than the partial structures of the CGH auxiliary structures.In one embodiment, after generating a first image of a first part of the CGH auxiliary structure in a first partial region of the final substrate, a second image of a second part of the CGH auxiliary structure is generated in a second partial region of the final substrate, wherein the second part of the CGH auxiliary structure is aligned relative to the first image during the generation of the second image. It has been found that by such an alignment on the basis of a previously generated image, a highly accurate positioning of the images relative to one another is possible, so that the accuracy which was achieved when the parts of the CGH auxiliary structure were generated with the aid of the direct writing lithography method can be maintained to a high degree. The first portion and the second portion may be immediately adjacent to each other to facilitate alignment.In the manner described above, a highly accurate image of the entire CGH auxiliary structure can be generated on the final substrate, which is then converted into a corresponding CGH structure by means of fundamentally known methods for structurization. In this case, it can furthermore be provided that the first image comprises at least one first optical marker, wherein the second part of the CGH auxiliary structure comprises at least one second optical marker, wherein the first optical marker and the second optical marker are used for aligning the second part of the CGH auxiliary structure relative to the first image.In an alternative embodiment, after the generation of a first image of a first part of the CGH auxiliary structure in a first sub-region, a first CGH sub-structure corresponding to a first sub-design is first generated in the first sub-region on the basis of the first image. This can be done, for example, by covering all partial regions of the final substrate that are different from the first partial region with a protective layer, so that a copolymerization method applied to the first partial region, with which method the first image is converted into the first CGH partial structure, has no influence on the other partial regions. In particular, the protective layer can be a lacquer layer which is applied to the substrate in the context of the process for structurizing (for producing the first subregion). The lacquer layer is thus structured in the first sub-region and used for producing the first CGH sub-structure, while the lacquer layer in all other sub-regions remains unstructured and protects the substrate at these locations. Subsequently, a second image of a second part of the CGH auxiliary structure can be generated in a second partial region of the final substrate. The previously applied resist layer can be removed for this purpose and a new resist layer can be applied to the final substrate in order to produce the corresponding CGH substructure in the second subregion. During this production of the second CGH substructure, all partial regions which differ from the second partial region, including the already structured first partial region, can in turn be covered by a protective layer which can in turn be formed in particular by the unstructured lacquer layer itself used for producing the second CGH substructure. During the generation of the second image, the second part of the CGH auxiliary structure can be aligned relative to the first CGH sub-structure. In this embodiment, an image is thus initially converted into a corresponding substructure before a further image is generated. In this embodiment as well, the first partial region and the second partial region can bear directly against one another in order to simplify the alignment. Furthermore, it can also be provided in this embodiment that the first CGH substructure comprises at least one first optical marker, wherein the second part of the CGH auxiliary structure comprises at least one second optical marker, wherein the first optical marker and the second optical marker are used for aligning the second part of the CGH auxiliary structure relative to the first CGH substructure.The subsubstrates can be rectangular. Furthermore, the subsubstrates can have a side length which is between 5 cm and 40 cm, in particular between 10 cm and 20 cm. Standardized electron beam lithography apparatuses are available for processing 6-inch substrates, which provide both a high writing speed and a high positional accuracy. The subsubstrates can therefore have a side length of 6 inches (about 152 mm), in particular, in order to be able to be used in such standard installations. A thickness of the sub-substrates may be less than 20 mm.Advantageous embodiments of the invention are described below by way of example with reference to the drawings.The following are shown: FIG. 1 : shows a device for interferometrically determining a fit error of an optical surface with an optical test element produced according to the invention; FIG. 2 : shows a schematic illustration of a CGH design determined within the scope of the production method according to the invention; FIG. 3 : shows an auxiliary substrate used in the context of the production method according to the invention in a cross-sectional view; FIG. 4 : shows a cross-sectional view of an auxiliary substrate used in the context of the production method according to the invention, having a CGH auxiliary structure; FIG. 5 : a final substrate with coatings used in the context of the production method according to the invention in a cross-sectional view; FIG. 6 : shows a schematic cross-sectional illustration of the auxiliary substrate of FIG. 4 and of the final substrate of FIG. 5 during the execution of a nanoimprint lithography method; FIG. 7 : a cross-sectional illustration of the final substrate after production of a CGH structure; FIG. 8 : shows a schematic illustration of a CGH design determined within the scope of an alternative embodiment of the production method according to the invention, which is divided into a plurality of partial designs; FIG. 9 : shows a schematic illustration of a part design, a part substrate and a part of a CGH auxiliary structure; FIG. 10 : shows a schematic cross-sectional illustration of an auxiliary substrate and a final substrate during the execution of a nanoimprint lithography method; FIG. 11 : shows a cross-sectional illustration of the final substrate of FIG. 10 after production of a CGH structure; FIG. 12 is a cross-sectional view of an alternative CGH auxiliary structure, which is designed as a shadow mask.FIG. 1 shows a schematic illustration of a device for interferometrically determining a fit error of an optical surface, in which an optical test element 19 produced according to the invention is used. The device comprises a light source 14, which in the exemplary embodiment is designed as an outlet end of a light guide. The light guide is fed from a laser light source, which in the present case is a helium-neon laser with a wavelength of approximately 633 nm. The beam path 15 emerging from the light guide in divergent state passes through a beam splitter 16 and is collimated by a collimator 17.The collimated beam path impinges on a Fizeau plate 18 at which the light is partially reflected. The reflected portions of the light form a reference beam path. The non-reflected portions of the light form a test beam path.The test beam path passes through the optical test element 19, impinges on an optical surface 20 of a mirror test piece and is reflected into itself. The reflected test beam path interferes with the reference beam path and is guided via the beam splitter 16, a diaphragm 21 and an eyepiece 22 to a detector 23 in the form of a CCD camera. The detector 23 records an interferogram from which the fit error in the examined optical surface 20 of the first mirror sample can be read.The test beam path which impinges on the optical test element 19 as an input wave in the form of a planar wavefront is transferred in the optical test element 19 into an output wave which forms a wavefront matched to the surface shape of the optical surface 20 of the mirror test piece. The output shaft is shaped such that it impinges perpendicularly on the entire optical surface 20 of the mirror test piece to be examined, provided that the mirror test piece corresponds to its desired shape and is arranged in its desired position relative to the optical test element 19. The mirror sample has a size of about 420 mm and is convexly curved. Due to the convex curvature, the test beam path reflected at the optical surface 20 widens in the direction of the optical test element 19. It is indeed possible to place the optical test element 19 in the vicinity of the optical surface 20 so that the reflected test beam path does not expand too much as far as the optical test element 19. However, the diameter of the optical inspection element 19 must have a diameter at least as large as that of the optical surface in order to allow a complete measurement of the optical surface. In the present case, the diameter of the optical test element is 450 mm. FIG. 1 schematically shows a CGH structure on the side of the optical test element 19 facing the mirror test piece 20.To produce the optical test element 19, a CGH design 24, which is suitable for measuring the optical surface 20, is initially determined by calculation in a manner which is known in principle. The CGH design is schematically illustrated in Figure 2. On the basis of the CGH design 24, a CGH structure 50 is produced on a final substrate 40 with the aid of the method (see FIG. 7 ). In the present case, a quartz glass substrate with a thickness of approximately 80 mm and a diameter of 450 mm is used as the final substrate 40. The CGH structure 50 to be produced is formed in the present case by a sequence of elevations and intermediate spaces therebetween. In FIG. 2, the position of the protrusions is illustrated by white lines and the position of the spaces is illustrated by black lines.The substrate 40 may have a diameter to thickness ratio that is between 4 and 10, and may be, for example, 6, 8, or 10. This gives the substrate 40 or the test element 19 produced therefrom sufficient stability. If the optical test element 19 is too thin, there is the risk that it will flex and the interferometric measurement will be adulterated as a result. Due to the large dimensions of the substrate 40, available direct writing lithography methods, in particular electron beam lithography methods, are unsuitable for structuring the substrate 40. The optical test element 19 was therefore produced in the present case with the aid of the method described below.The method is illustrated with reference to FIGS. 3-7. Within the scope of the method according to the invention, an auxiliary substrate 30 is provided, which is shown in a cross-sectional view in FIG. 3. The auxiliary substrate 30 is made of transparent quartz glass and has a thickness of at least 5 mm, in particular at least 15 mm, preferably at least 25 mm. A hard mask 31, for example made of chromium, is applied to the auxiliary substrate 30. The hard mask is covered with a resist 32 suitable for electron beam lithography. With the aid of an electron beam lithography method, an image of a CGH auxiliary structure is first produced in the varnish 32. Since the auxiliary substrate 30 is significantly thinner and thus significantly lighter than the final substrate 40, this process can be carried out significantly more quickly and with a significantly higher positional accuracy compared to a case in which the CGH structure is produced directly on the final substrate 40 by means of electron beam lithography.On the basis of the image, the CGH auxiliary structure 25 is subsequently produced on the auxiliary substrate 30 (see FIG. 4 ). A method for copolymerization suitable for this purpose, in which, among other things, the auxiliary substrate 30 is selectively etched and the hard mask is subsequently removed, is fundamentally known and therefore does not need to be explained in detail here.The auxiliary substrate 30 with the CGH auxiliary structure 25 located thereon is then used as a stamp in the course of a nanoimprint lithography method in order to produce an image of the CGH auxiliary structure 25 on the final substrate 40. For this purpose, the final substrate 40 is coated with a hard mask 41 and with a lacquer 42 suitable for nanoimprint lithography (see FIG. 5 ). The lacquer 42 has a certain viscosity, so that an image of the CGH auxiliary structure 25 formed by a depth profile is embossed into the lacquer 42 when the CGH auxiliary structure 25 is brought into surface contact with the lacquer 42 (cf. FIG. 6 ). After the paint has cured, the CGH auxiliary structure can be removed and the image is retained in the paint. The curing process can be assisted, for example, by irradiation with UV light. On the basis of the depth profile embossed into the varnish 42, a CGH structure 50 corresponding to the CGH design 24 can subsequently be produced on the final substrate 40 (cf. FIG. 7 ). This can likewise be effected with the aid of known methods for structurization.With reference to FIGS. 8-11, an alternative embodiment of the production method according to the invention is explained below. In this embodiment of the method, a particularly large optical test element having a diameter of at least 500 mm, in particular at least 600 mm, and having a thickness of at least 60 mm, at least 70 mm or at least 80 mm is produced. In this embodiment too, a CGH design 24, which is suitable for measuring an optical surface, is initially determined by calculation in a manner which is known in principle. In contrast to the embodiment of FIGS. 2, 3, 4, 5, 6 to 7, this CGH design 24 is initially divided into a number of 16 partial designs 241 in the present case.Subsequently, a number of 16 subsubstrates 301 is provided, wherein one of the subsubstrates 301 is respectively assigned to one of the sub-designs 241. The sub-substrates 301 are square and have a side length of 152 mm (about 6 inches) and a thickness of 10 mm. The partial designs 241 may have a maximum side length of at most 200 mm, in particular at most 150 mm, further in particular at most 100 mm. In the present case, the side length of the sub-design 241 is smaller (for example 140 mm) than the side length of the sub-substrates, so that the sub-designs 241 can each be applied completely to one of the sub-substrates 301 in each case, leaving one edge free.In the manner already described in connection with FIGS. 3 and 4, a first of the sub-designs 241 is first used to generate a corresponding first part 251 of a CGH auxiliary structure on a first sub-substrate 301. This is schematically illustrated in FIG. 9. This process is repeated for each of the further 15 subsubstrates, so that different parts of the entire CGH auxiliary structure 25 are respectively produced on the 16 subsubstrates. Since the subsubstrates in the present case have a side length of 152 mm (about 6 inches), standardized electron beam lithography apparatuses can be used to produce the respective parts of the CGH auxiliary structure 25. The parts of the CGH auxiliary structure 25 can therefore be produced in an acceptable time and with the highest precision.A final substrate 40 is then provided (cf. FIG. 10 ) and is prepared in the manner already described in connection with FIG. 5 for carrying out a nanoimprint lithography method. The first part 251 of the CGH auxiliary structure 25 shown in FIG. 9 is used as a stamp in the context of the nanoimprint lithography method in order to generate an image of the first part 251 of the CGH auxiliary structure 25 in the varnish 42 in a first partial region 401 of the final substrate 40. In FIG. 10, a corresponding image is schematically illustrated in the first partial region 401 on the left side of the substrate 40, wherein the first part 251 of the CGH auxiliary structure 25 has already been removed again.Subsequently, a corresponding image of the second part 252 is generated in an analogous manner in a second part region 402 adjacent to the first part region 401 with the aid of a second part substrate 302 and the second part 252 of the CGH auxiliary structure 25 located thereon. FIG. 10 shows the second sub-substrate 302 shortly before it is brought into contact with the varnish 42. The second subsubstrate 302 used as a stamp is aligned relative to the image of the first part 251 of the CGH auxiliary structure located in the first subregion 401. In an edge region 303, the subsubstrates can have optical markers which can be aligned with previously generated optical markers in the edge region of a generated image.The process is repeated until images of all 16 parts of the CGH assist pattern are present in corresponding further portions of the substrate 40. Subsequently, in a manner analogous to that described in connection with FIGS. 6 and 7, the CGH structure 50 can be produced in the final substrate 40. This is illustrated in FIG. 11, in which the parts 501- 504 of the CGH structure 50 produced in the sub-regions 401- 404 are shown in a cross-sectional view.Alternatively, it is also possible that after the generation of a first image of a first part 251 of the CGH auxiliary structure, the remaining partial regions are covered with a protective layer in the first partial region 401, and the first part 501 of the CGH structure is first produced in the first partial region 401. The protective layer ensures that the method steps used in this case lead to structuring of the substrate 40 only in the first partial region 401. During a subsequent structuring of the second partial region 402 of the substrate 40, the second partial substrate 302 can be aligned on the basis of the already produced first part 501 of the CGH structure 50. During the production of the second part 502 of the CGH structure, the already structured first part 501 of the CGH structure and the still unstructured subareas of the substrate 40 are covered with a protective layer. Also in this embodiment, optical markers may be used to increase alignment accuracy.As already mentioned above, the CGH structure 50 to be produced is formed in the embodiments of FIGS. 2, 3, 4, 5, 6, 7, 8, 9, 10 to 11 by a sequence of elevations with intermediate spaces between them. The CGH structure is thereby created by removing a portion of the final substrate 40 by a selective etching process. Alternatively, the CGH structure 50 can also be formed by a sequence of opaque and transparent regions. Corresponding copolymerization methods for producing such a sequence are known in principle, so that a detailed description can be omitted here.In the production methods explained above, instead of nanoimprint lithography, an X-ray lithography method can be used to transfer the CGH auxiliary structure 25 or the parts 251, 252 of the CGH auxiliary structure 25 to the final substrate 40. For this purpose, instead of a stamp, a shadow mask forming the CGH auxiliary structure 25 can be produced in the CGH auxiliary substrate 30. A corresponding CGH auxiliary structure 25 designed as a shadow mask is illustrated in a cross-sectional view in FIG. 12. The shadow mask may have through-holes or a sequence of transparent and opaque regions. Instead of the nanoimprint lithography method illustrated in FIG. 6, the X-ray lithography method is carried out by positioning the shadow mask in the immediate vicinity of or in contact with the final substrate 40 and transferring the CGH auxiliary structure 25 to the final substrate 40 by exposure of the shadow mask to X-ray radiation in a manner known in principle.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedWO 2005 / 114101 A1

[0002] DE 10 2015 202 695 A1

[0002] DE 10 2012 217 800 A1

[0002] DE 10 2019 204 096 A1

[0002] U.S. Pat. No. 8,941,837 B1

[0005]

Claims

Method for producing an optical test element (19) for determining a fit error of an optical surface (20), comprising the following steps: - determining a CGH design (24) suitable for measuring the optical surface (20), - generating a CGH auxiliary structure (25) corresponding to the CGH design (24) on an auxiliary substrate (30) with the aid of a direct writing lithography method, - generating an image of the CGH auxiliary structure (25) on a final substrate (40) with the aid of a transmitting lithography method, - producing a CGH structure (50) corresponding to the CGH design (24) on the basis of the generated image.Method according to claim 1, wherein the auxiliary substrate (30) has a lower mass than the final substrate (40).The method according to claim 1 or 2, wherein the auxiliary substrate (30) has a thickness less than the final substrate (40), wherein a thickness of the auxiliary substrate (30) is preferably less than or equal to 20 mm.Method according to any one of claims 1 to 3, wherein the final substrate (40) has a diameter and a thickness, wherein a ratio of the diameter to the thickness is between 3:1 and 10:1, preferably between 4:1 and 6:1.The method according to any one of claims 1 to 4, wherein the transmissive lithography method is selected from the group comprising nanoimprint lithography and X-ray lithography.The method according to any one of claims 1 to 5, wherein the direct writing lithography for creating the CGH assist pattern (25) is selected from electron beam lithography and laser beam lithography.Method according to one of Claims 1 to 6, in which the determined CGH design (24) is divided into a number of sub-designs (241), the auxiliary substrate (30) being formed by a number of sub-substrates (301), wherein the production of the CGH auxiliary structure comprises a part (251, 252) of the CGH auxiliary structure being produced in each case on the sub-substrates (301) using in each case one of the sub-designs (241).Method according to Claim 7, in which the generation of an image of the CGH auxiliary structure takes place by generating images of the parts (251, 252) of the CGH auxiliary structure in subareas (401, 402, 403, 404) of the final substrate (40).Method according to Claim 8, in which, after the generation of a first image of a first part (251) of the CGH auxiliary structure in a first subregion (401), a second image of a second part (252) of the CGH auxiliary structure is generated in a second subregion (402), wherein the second part (252) of the CGH auxiliary structure is aligned relative to the first image during the generation of the second image.The method of claim 9, wherein the first image comprises at least one first optical marker, wherein the second portion (252) of the CGH auxiliary structure comprises at least one second optical marker, wherein the first optical marker and the second optical marker are used to align the second portion (252) of the CGH auxiliary structure relative to the first image.Method according to Claim 8, in which, after the generation of a first image of a first part (251) of the CGH auxiliary structure in a first sub-region (401) on the basis of the first image, firstly a first CGH sub-structure (501) corresponding to a first sub-design (241) is generated in the first sub-region (401), wherein subsequently a second image of a second part (252) of the CGH auxiliary structure is generated in a second sub-region (402), and wherein the second part (252) of the CGH auxiliary structure is aligned relative to the first CGH sub-structure (501) during the generation of the second image.The method of claim 11, wherein the first CGH substructure (501) comprises at least one first optical marker, wherein the second part (252) of the CGH auxiliary structure comprises at least one second optical marker, wherein the first optical marker and the second optical marker are used to align the second part (252) of the CGH auxiliary structure relative to the first CGH substructure (501).Method according to one of Claims 7 to 12, in which the number of part designs is between 2 and 36, preferably between 4 and 16.Method according to one of claims 7 to 13, wherein the sub-substrates (301) have a side length which is between 5 cm and 40 cm, preferably between 10 cm and 20 cm and more preferably is about 152 mm.Method according to one of Claims 7 to 14, in which the subsubstrates have a thickness which is less than 20 mm.Optical test element (19) for determining a fit error of an optical surface (20), comprising a substrate (40) with a CGH structure (50) produced thereon, characterized in that the optical test element (19) is produced by a method according to one of Claims 1 to 15.

Images