Mirror and mirror substrate, and method and device for the production thereof

Abstract

The present invention relates generally to mirrors and mirror substrates, in particular mirrors and mirror substrates having high aspect ratios, as well as methods and apparatus for producing the same.

Description

[0001] This application is a divisional application of patent application 201910729737.X filed on August 8, 2019, with the invention name of "Reflector and reflector substrate and method and device for producing the same". Technical Field

[0002] The present invention generally relates to a mirror and a mirror substrate, in particular a mirror and a mirror substrate having a high aspect ratio, and a method and apparatus for producing the same. Background Art

[0003] Mirror substrates are used, for example, in so-called reflecting telescopes (also called reflectors) or in other precision optics, where they serve as substrate for applying highly reflective mirror layers.

[0004] For consistently high quality mirrors, especially mirrors with long-term stability, the properties of the mirror substrate play an important role:

[0005] -The weight of the reflector substrate

[0006] If the weight of the mirror substrate is too high, for example because it is a mirror with a particularly large diameter, deformations may occur under the inherent weight of the mirror substrate, which will reduce the quality of the optical image. However, a low weight is generally beneficial even for smaller mirror substrates due to improved handling.

[0007] -Surface quality of the reflector substrate

[0008] A mirror substrate with a high surface quality is required in order to be able to deposit a high-quality reflective layer. Of particular importance is the roughness of the mirror surface of the mirror substrate, on which the highly reflective layer is deposited.

[0009] -Other performance

[0010] In addition, the reflector substrate should be essentially made of a highly resistant material, in particular a highly heat-resistant material, and which has a low coefficient of thermal expansion. Suitable materials include in particular glass, ceramics and glass ceramics. Typically, the thermal expansion of the material is determined by a static method in which the length of the specimen is measured at the beginning and end of a specific temperature interval and the coefficient of expansion α or CTE (coefficient of thermal expansion) is calculated from the difference in length. The CTE is then reported as an average value for the temperature interval - for example, for a temperature interval of 0°C to 50°C, it is referred to as CTE (0; 50) or α (0; 50). Known materials for precision components with zero expansion in a temperature range of about room temperature are ceramics, Ti-doped fused silica SiO2 and glass ceramics. Glass ceramics are in particular lithium aluminum silicate glass ceramics (LAS glass ceramics), which are described, for example, in US Pat. No. 4,851,372, US Pat. No. 5,591,682, EP 587979, US Pat. No. 7,226,881, US Pat. No. 7,645,714 and DE 10 2004 008 824 A1.

[0011] In addition, for example, it is known that: or Lithium aluminosilicate glass ceramics sold as such; or cordierite-based materials; or glasses having a very low coefficient of thermal expansion, such as synthetic fused silica doped with TiO2, such as those sold under the trademark Glass for sale; or a ceramic containing or consisting of cordierite or SiC.

[0012] Usually, reflector substrates, for example made of glass ceramics, are produced by first providing a melt and then casting the material, so first a glassy material is provided. In order to avoid cracks in the material and produce glass ceramics from glassy raw materials, complex temperature control, in particular slow and controlled cooling, is required. Similarly, in the production of synthetic fused silica, so-called ingots or larger plates are first produced by depositing SiO2. If necessary, the diameter of the plate can be increased by reducing the process.

[0013] Subsequently, mechanical reworking is performed to obtain a workpiece with the desired dimensions and the desired quality. Mechanical reworking can include drilling, grinding and polishing, among others.

[0014] It is known to use supports arranged under the workpiece or the reflector substrate, respectively, to carry out these re-processing steps. Damage to the reflector substrate can be prevented by using these supports.

[0015] In particular, it is known that workpieces with a high aspect ratio, such as mirror substrates with a high aspect ratio, should preferably be supported over the entire surface of the workpiece during mechanical reprocessing, but also during other reprocessing steps such as coating, or when being transported. Such full-surface support of the workpiece is intended in particular to keep the workpiece, i.e., for example, a mirror substrate, dimensionally stable so that it does not deform, for example, under the influence of gravity.

[0016] For example, German patent application DE 10 2015 112 036 A1 discloses a mineral-based casting support for full-surface support of a workpiece having a high aspect ratio.

[0017] However, it has been found that problems arise with such mineral-based cast supports if extensive polishing processes are required to obtain a surface of a certain quality. In this case, a large amount of heat is generated. However, this is disadvantageous for the different thermal expansions between the supported workpiece made of a low-expansion material and the mineral-based cast support, making it even less possible to achieve the required accuracy in terms of the geometric dimensions of the mirror substrate and its surface quality.

[0018] European patent application EP 1 391 433 A2 discloses a support made of keatnet glass ceramics, which can be used to shape, for example, glass or glass ceramics. However, keatnet glass ceramics still have a higher coefficient of thermal expansion than the usual low-expansion materials used for reflector substrates. Therefore, it is also impossible to produce reflector substrates with the required accuracy in terms of geometric dimensions and surface quality in this way.

[0019] These problems occur in particular when developing novel reflector substrates which have a particularly small thickness and a large diameter at the same time. Currently, such reflector substrates cannot be put into production, or they do not have sufficient quality in terms of shape stability and surface quality, or they may even break during processing.

[0020] Therefore, there is a need for a reflector substrate and a reflector with a high aspect ratio and a small absolute thickness, a high surface quality and a high dimensional accuracy and a high stability. In addition, there is a need for a support that can be used to manufacture a reflector substrate and a reflector with a high aspect ratio, and a method for producing such a reflector substrate and a reflector. Summary of the invention

[0021] The object of the present invention is to provide a reflector substrate which overcomes or at least alleviates the known drawbacks of the prior art, and in particular to provide a reflector based on such a reflector substrate. There is also a need for a method and apparatus for producing such a reflector substrate and a reflector based on such a reflector substrate.

[0022] The objects of the invention are achieved by the subject-matter of the independent claims. Preferred embodiments and special embodiments are defined by the dependent claims.

[0023] The reflector substrate according to the present invention comprises an average linear thermal expansion coefficient less than or equal to 1*10 -6 / K, preferably less than or equal to 0.1*10 -6 / K, and most preferably less than or equal to 0.05*10 -6 According to a particularly advantageous embodiment, the average linear thermal expansion coefficient of the reflector substrate can even be less than or equal to 0.02*10 -6 / K or even less than or equal to 0.01*10 -6 / K.

[0024] The reflector substrate has at least one of the following features:

[0025] The ratio of the lateral dimension of the reflector substrate to its maximum thickness is at least 100, preferably at least 150, more preferably at least 200, and most preferably 300 or more;

[0026] The weight per unit area of ​​the reflector substrate is 100 kg / m 2 or less, preferably 50kg / m 2 or less, more preferably 30kg / m 2 , and most preferably 15kg / m 2 or smaller.

[0027] The reflector substrate has a mirror surface, and the roughness of the mirror surface is R a The mirror surface of the reflector substrate preferably has a ground finish surface. Ra is the arithmetic mean of the filtered roughness distribution determined by the deviation about the center line within the evaluation length. The root mean square RMS is defined as the square root of the mean square (the arithmetic mean of the squares of a set of numbers). Distribution roughness parameters such as Ra and RMS are included in ISO 4287:1997.

[0028] According to one embodiment of the present invention, the maximum thickness of the reflector substrate is 50 mm or less, 20 mm or less, preferably 15 mm or less, more preferably 10 mm or less, and most preferably 2 mm or less.

[0029] Preferably, the lateral dimensions of the mirror substrate are at least 200 mm and / or at most 4500 mm. However, the invention is equally applicable to mirror substrates having smaller or larger lateral dimensions.

[0030] According to another embodiment of the invention, the mirror substrate may be polished on the support such that the mirror substrate will have a polished mirror surface having a root mean square (RMS) roughness of less than 2 nm, preferably less than 1 nm.

[0031] The following definitions and terms apply in the context of this application.

[0032] A reflector substrate material having a low thermal expansion coefficient is one that exhibits an average linear thermal expansion coefficient less than or equal to 3*10 -6 / K material.

[0033] The ratio of the lateral dimension of the mirror substrate to its maximum thickness is also referred to as the aspect ratio. The aspect ratio is therefore a dimensionless parameter. Typically, the mirror substrate has a circular or approximately circular shape, so that the lateral dimension is typically the diameter of the mirror substrate. If the mirror substrate has different lateral dimensions, for example, if the mirror substrate has a different width than its length, the average value is calculated and used for the calculation of the aspect ratio.

[0034] The thickness of the reflector substrate may vary across the entire reflector substrate. For example, the thickness of the reflector substrate at the outer edges may be less than the thickness at its center. To determine the aspect ratio, the maximum thickness is used.

[0035] A high aspect ratio generally means a lower weight per unit area. In one embodiment of the present invention, the weight per unit area is 100 kg / m 2 or less, preferably 50kg / m 2 or less, and most preferably 30 kg / m 2 or smaller.

[0036] In the present application, unless explicitly stated otherwise, the average coefficient of thermal expansion α is specified in the range of 0 to 50°C, however, the present invention also relates to materials with low thermal expansion, whose expansion coefficient is measured in different temperature ranges. This value is the nominal average linear thermal expansion coefficient in accordance with ISO 7991, which is determined by static measurement. In the context of the present invention, unless explicitly stated otherwise, the terms expansion coefficient, thermal expansion coefficient, average linear thermal expansion coefficient and α can be used interchangeably.

[0037] In the present invention, a mirror substrate is understood to mean a substrate on which a highly reflective layer (or mirror layer) is applied. The term mirror substrate also includes workpieces to be processed or being processed into a mirror substrate, i.e. semi-finished products such as mirror substrates, which, although they have been cut to the size of the finished mirror substrate, still have to undergo further reprocessing steps.

[0038] In the context of the present invention, a reflector refers to a combination of a reflector substrate and a high reflective layer on its functional surface. The surface of the reflector substrate on which the reflective layer is applied is referred to as the functional surface of the reflector substrate in the present disclosure. In the context of the present invention, the high reflective layer is also referred to as a mirror layer.

[0039] A support is understood to mean a device which serves for supporting purposes during storage, during transport and / or during further processing of a workpiece carried thereon, for example a mirror substrate.

[0040] In the context of the present invention, if an article is described as comprising a specific material, this also includes in particular the case where the article is mainly made of this material, that is to say more than 50 wt % is made of this material, or even substantially made of this material, that is to say more than 90 wt % is made of this material. In addition, this may also include the case where the article consists of this material, that is to say is completely made of this material.

[0041] In the context of the present invention, the mirror surface of the mirror substrate refers to the surface of the mirror substrate on which the mirror layer will be applied or has been applied. Therefore, this is the quality surface of the mirror substrate, that is, the surface on which special requirements are placed in terms of surface quality.

[0042] The reflector substrate thus comprises a material with a low average linear thermal expansion coefficient. In particular, the reflector substrate can consist essentially of this material or a mixture of such materials, that is to say more than 50 wt % of this material or a mixture of such materials; or even essentially of this material or a mixture of such materials, that is to say more than 90 wt % of this material or a mixture of such materials; or even completely of this material or a mixture of such materials. Materials with such a low thermal expansion coefficient include in particular glasses, glass ceramics and ceramics; for example lithium aluminosilicate glass ceramics, such as those sold under the trademark or Lithium aluminosilicate glass ceramics sold; for example, or cordierite-based materials; or glasses with very low thermal expansion coefficients, such as synthetic fused silica doped with TiO2, for example, sold under the trademark Glass for sale; or ceramics containing or made of cordierite or SiC.

[0043] Until now, it has not been possible to provide a mirror substrate according to the invention, i.e. a mirror substrate comprising a material having a low coefficient of thermal expansion and the following characteristics:

[0044] An aspect ratio of at least 100, preferably at least 150, more preferably at least 200, and most preferably 300 or more;

[0045] and / or

[0046] The weight per unit area of ​​the reflector substrate is 100 kg / m 2 or less, preferably 50kg / m 2 or less, and more preferably 30 kg / m 2 or smaller;

[0047] The reflector substrate has a roughness R a It is a mirror surface with a thickness of at most 3.5 μm, preferably less than 1.2 μm.

[0048] In particular, it has hitherto not been possible to achieve a maximum thickness of the mirror substrate of 20 mm or less, preferably 15 mm or less, more preferably 10 mm or less and most preferably 2 mm or less.

[0049] This is especially true for mirror substrates with lateral dimensions of at least 200 mm. For mirror substrates with lateral dimensions of 1000 mm or more, a maximum thickness of 50 mm or less, in particular 40 mm or less or more preferably 30 mm, cannot be achieved.

[0050] That is, due to the large aspect ratio and small absolute thickness, it is impossible to process the surface of the reflector substrate to achieve a low roughness R of not more than 3.5 μm or even not more than 1.2 μm. a In particular, it is not possible to achieve such a roughness in a grinding process. Instead, in the machining of such mirror substrates, the mirror substrates already break during remachining before such a low roughness is achieved.

[0051] According to one embodiment, the roughness R of the mirror surface is a Not greater than 3.5 μm, preferably not greater than 1.2 μm, and the functional surface of the mirror substrate preferably has a ground surface finish.

[0052] So far, this is not feasible.

[0053] In particular, difficulties in manufacturing such a mirror substrate include the fact that the reprocessing processes (e.g. grinding, lapping or polishing) for achieving the low roughness considered here release a large amount of thermal energy. Therefore, in other words, both the mirror substrate and the support used in the reprocessing process heat up. This heating is such that, in the process required here, thermomechanical stresses may arise between the support and the mirror substrate carried thereon, and this will occur in particular if the support has a high coefficient of thermal expansion.

[0054] According to another embodiment of the present invention, the reflector substrate includes: glass ceramics, preferably lithium aluminum silicate glass ceramics, and the lithium aluminum silicate glass ceramics are preferably in the form of high quartz solid solution glass ceramics; or Ti-doped synthetic silica glass; and / or ceramics, preferably ceramics containing cordierite and / or SiC.

[0055] In particular, the mirror substrate can consist predominantly of this material, that is to say more than 50 wt % of this material; or essentially of this material, that is to say more than 90 wt % of this material; or even completely of this material.

[0056] Such materials generally exhibit not only a low coefficient of thermal expansion, but also generally good reprocessability, such as good grindability and polishability.

[0057] According to another aspect, the present invention further relates to a reflector, in particular a reflector comprising a reflector substrate according to an embodiment of the present invention. The reflector comprises a high-reflection layer on a mirror surface of the reflector substrate.

[0058] Another aspect of the invention relates to a support for supporting a reflector substrate, in particular a reflector substrate according to an embodiment of the invention, preferably over its entire surface, on which the reflector substrate is carried during its processing and / or transportation. The support comprises a mean linear thermal expansion coefficient of less than or equal to 1*10 -6 / K, preferably less than or equal to 0.1*10 -6 / K, and most preferably less than or equal to 0.05*10 -6 / K material. According to certain embodiments, the expansion coefficient of the support member can even be less than or equal to 0.02*10 -6 / K, or even less than or equal to 0.01*10 -6 / K.

[0059] In particular, the support may consist mainly of this material or a mixture of such materials, that is to say more than 50 wt % of this material or a mixture of such materials; or even substantially of this material or a mixture of such materials, that is to say more than 90 wt % of this material or a mixture of such materials; or even completely of this material or a mixture of such materials. Preferably, the lateral dimension of the support is generally at least 200 mm and at most 4500 mm.

[0060] Therefore, the support is suitable for processing and / or transporting mirror substrates having large lateral dimensions. At the same time, the average linear thermal expansion coefficient is less than or equal to 1*10 -6 / K, preferably less than or equal to 0.1*10 -6 / K, and most preferably less than or equal to 0.05*10 -6 / K (and according to certain embodiments, even less than or equal to 0.02*10 -6 / K or even less than or equal to 0.01*10 -6 The material of the support element of 1000 Å / K ensures that even if a large amount of heat is generated during reprocessing (such as grinding, lapping or polishing), the support element will only show low thermal expansion.

[0061] Here, the surface of the support refers to the surface of the support which at least partially bears the mirror substrate during further processing and / or when being transported.

[0062] According to another embodiment of the support, the surface of the support has a curved shape.Preferably, the surface of the support approximates the envelope surface.

[0063] Here, an envelope surface can be understood as a predetermined shape or geometry of the surface of the support. The quality of the support is therefore also characterized by any existing deviations between the actual surface of the support and the ideal descriptive envelope surface. The final deviation that is still tolerable between the envelope surface and the actual surface varies depending on the diameter of the workpiece or mirror substrate.

[0064] Particularly preferably, the deviation between the support and the envelope surface is:

[0065] For a mirror substrate having a lateral dimension of at least 4000 mm, the deviation is no greater than 0.5 mm, preferably no greater than 0.1 mm, more preferably no greater than 0.05 mm, and according to some embodiments even no greater than 0.025 mm;

[0066] and / or

[0067] For a mirror substrate having a lateral dimension of at least 2000 mm, the deviation is no greater than 0.2 mm, preferably no greater than 0.05 mm, and more preferably no greater than 0.025 mm;

[0068] and / or

[0069] For a mirror substrate having a lateral dimension of at least 1200 mm, the deviation is no greater than 0.1 mm, preferably no greater than 0.05 mm, and more preferably no greater than 0.01 mm.

[0070] According to another embodiment of the support, the surface of the support is at least partially covered by an intermediate material. The intermediate material may be a film, according to one embodiment a polymer film. The intermediate material may also comprise bitumen, asphalt and / or polysiloxane. Preferably, the thickness of the intermediate material (e.g. a film) is at least as great as the deviation between the actual shape of the surface and the envelope surface. Particularly preferably, the maximum thickness of the intermediate material (e.g. a film) is at most 200 μm, preferably at most 100 μm, more preferably at most 50 μm, or even most preferably only at most 25 μm. Here, it is advantageous that the shape of the support is very well adapted to the envelope surface of the reflector substrate.

[0071] Polymer films may exhibit nonlinear elastic properties, which may ultimately result in deviations in the shape of the reflective surface of the reflector substrate after grinding. Optionally, this situation can be improved by using optional or additional intermediate materials. Such intermediate materials may include metal foils or paste-like or gel-like materials, as well as cured films.

[0072] The intermediate material may in particular serve to mitigate any deviations between the surface shape of the support and an ideal predetermined surface shape that can be described by the envelope surface.

[0073] However, alternatively or additionally, the intermediate material may also fulfil other functions. For example, the intermediate material may also be used to reduce the adhesion between the support and the carried mirror substrate, so that once the processing or transportation of the mirror substrate is completed, the mirror substrate can be easily, in particular without damage, lifted from the support.

[0074] If the intermediate material is provided in the form of a polymer film, the polymer may include one or more of the group consisting of polyethylene (PE), polypropylene (PP), polystyrene (PS), polycarbonate (PC), one or more polyesters, polyetherketone (PEK), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) (such as ), one or more tetrafluoroethylene copolymers (ETFE), polyvinyl chloride (PVC).

[0075] Preferably, the intermediate material includes a material designed to exhibit heat resistance of 150° C. or higher.

[0076] According to another embodiment of the invention, an intermediate material is preferred which has the lowest possible coefficient of thermal expansion for these material grades.

[0077] If the intermediate material is in the form of a polymer film, polymers that exhibit heat resistance of 150° C. or higher are preferred. Also in this case, polymers that have the lowest possible coefficient of thermal expansion are preferred.

[0078] According to another embodiment of the support, the intermediate material comprises polyvinyl chloride (PVC), PTFE, ETFE, PEK and / or PET. For example, the intermediate material can be in the form of a polymer film comprising PVC, PTFE, ETFE, PEK and / or PET. If lower thermal loads occur during the reprocessing step, polymer films with lower thermal stability can also be used, such as films made of polyethylene or polypropylene. In addition, thermoplastic polymer films are preferred, which tend to yield to a certain extent at high temperatures, which may occur during mechanical reprocessing of the reflector substrate. In this way, any deviations between the surface of the support and the envelope surface can be even better compensated.

[0079] The film may be applied to the surface of the substrate intactly as a whole or in the form of spaced-apart portions, for example in the form of individual pieces.

[0080] According to one embodiment, the film comprises "channels" extending at least to the edge so that when the mirror substrate is placed on a support, the air can dissipate to the outside and the mirror substrate will bear on the surface. If the film is applied as a whole, such channels (e.g. cuts) can be introduced into the film later.

[0081] According to another embodiment of the support, the surface of the support is partially covered by an intermediate material (e.g. a film) so that the intermediate material is applied to the surface in the form of spaced-apart portions. The spaced-apart portions of the intermediate material can be arranged in a symmetrical pattern. One option for this is radial symmetry, for example the portions of the intermediate material (e.g. portions of the film) are in a four-fold radially symmetrical pattern.

[0082] According to one embodiment, the portions have a circular or oval shape.

[0083] This embodiment of the support allows mechanical loads that occur during processing or transport of the mirror substrate, for example due to the inherent weight of the mirror substrate, to be absorbed particularly uniformly over the entire surface of the support. This minimizes mechanical stresses in the mirror substrate. Thus, the stability of the mirror substrate on the support during processing is increased.

[0084] According to a variant of the invention, the support can be configured so that any residues produced during remachining of the supported workpiece can be removed cleanly and without damaging the workpiece itself.

[0085] For this reason, the support may be configured in such a way that any residues produced during the machining of the workpiece can be discharged.

[0086] For this purpose, the surface of the support can, for example, be smooth or provided with grooves.

[0087] Furthermore, the surface of the support may comprise at least one opening, for example a drain opening, through which residues produced during the further processing of the workpiece can be drained. If one or more openings are provided, the intermediate material can even be applied closely or continuously, so that there can be no channels at the outer edge of the mirror substrate, e.g. Figure 3 as shown, since air and residue can dissipate through the openings in the support.

[0088] According to one embodiment of the invention, the discharge opening is defined by a mesh-like groove consisting of radially extending and circular elements.

[0089] Another aspect of the invention relates to an assembly consisting of a support and a reflector substrate.

[0090] The support is used to support the reflector substrate, preferably over its entire surface, the reflector substrate being carried on the support during its processing and / or transportation, and the support comprises an average linear thermal expansion coefficient of less than or equal to 1*10 -6 / K, preferably less than or equal to 0.1*10 -6 / K, and most preferably less than or equal to 0.05*10 -6 / K (according to a specific embodiment, even less than or equal to 0.02*10 -6 / K or even less than or equal to 0.01*10 -6 / K) materials.

[0091] The reflector substrate includes an average linear thermal expansion coefficient less than or equal to 1*10 -6 / K, preferably less than or equal to 0.1*10 -6 / K, and most preferably less than or equal to 0.05*10 -6 / K (according to a specific embodiment, even less than or equal to 0.02*10 -6 / K or even less than or equal to 0.01*10 -6 / K) materials.

[0092] Preferably, the maximum thickness of the mirror substrate is 50 mm or less, in particular 20 mm or less, preferably 15 mm or less, more preferably 10 mm or less, and most preferably 2 mm or less. The lateral dimension of the mirror substrate is preferably at least 200 mm.

[0093] The reflector substrate has one of the following characteristics:

[0094] The ratio of the lateral dimension of the reflector substrate to its maximum thickness is at least 100, preferably at least 150, more preferably at least 200, and most preferably 300 or more;

[0095] The weight per unit area of ​​the reflector substrate is 100 kg / m 2 or less, preferably 50kg / m 2 or less, more preferably 30kg / m 2 or less, and most preferably 15 kg / m 2 or smaller.

[0096] According to one embodiment of the assembly, the roughness R of the mirror surface of the reflector substrate a It is at most 3.5 μm, ideally less than 1.2 μm, and the mirror surface of the mirror substrate preferably has a ground surface finish.

[0097] According to another embodiment, the surface of the mirror substrate has an RMS roughness of less than 2 nm, preferably less than 1 nm, and the surface of the mirror substrate preferably has a polished surface finish.

[0098] According to another embodiment of the assembly, the thermal expansion coefficient of the material from which the support is made and the thermal expansion coefficient of the material from which the reflector substrate is made differ by an absolute value of no more than 1*10 -6 / K, preferably the absolute value is not greater than 0.1*10 -6 / K, preferably the absolute value is not greater than 0.05*10 -6 / K, and the absolute value is most preferably not greater than 0.02*10 -6 / K.

[0099] Preferably, the surface of the support and the surface of the reflector substrate carried on the surface of the support have opposing complementary curvatures.

[0100] In other words, when the surface of the mirror substrate carried on the support has a concave curvature, the surface of the support preferably has a convex curvature, and vice versa. Thus, the surface of the support and the carrying surface of the mirror substrate have complementary shapes in the overlapping area.

[0101] According to an embodiment of the assembly, the mirror substrate is laterally fixed to the support and preferably the mirror substrate is additionally secured against detachment from the support.

[0102] Another aspect of the present invention relates to a method for producing a reflector substrate, in particular a reflector substrate according to any one of the above embodiments. The method comprises the following steps:

[0103] providing a support for supporting, preferably over its entire surface, a reflector substrate carried thereon;

[0104] A reflector substrate is provided, wherein the reflector substrate has a thermal expansion coefficient less than or equal to 1*10 -6 / K, preferably less than or equal to 0.1*10 -6 / K, and most preferably less than or equal to 0.05*10 -6 / Made of K material;

[0105] placing a reflector substrate onto a support;

[0106] Mechanical reworking of the surface of a reflector substrate, in particular its mirror surface, in particular polishing, drilling, grinding or lapping;

[0107] The absolute value of the difference between the thermal expansion coefficient of the material of the support and the thermal expansion coefficient of the material of the reflector substrate is not greater than 1*10 -6 / K, preferably the absolute value is not greater than 0.1*10 -6 / K, preferably the absolute value is not greater than 0.05*10 -6 / K, and the absolute value is most preferably not greater than 0.02*10 -6 / K.

[0108] According to a particular embodiment of the method, the thermal expansion coefficient of the material of which the reflector substrate is made can even be less than or equal to 0.02*10 -6 / K or even less than or equal to 0.01*10 -6 / K.

[0109] The functional surface of the reflector substrate is arranged opposite to the surface carried on the support. In a preferred embodiment, for safe processing and / or safe transportation of the reflector substrate, the reflector substrate is fixed to the support to at least prevent lateral displacement relative to the support. Preferably, the reflector substrate is also fastened or fixed to prevent lifting or detachment from the support. The fixing can be achieved in particular by a clamp, by bonding or by negative pressure between the support and the reflector substrate.

[0110] Another aspect of the invention relates to the use of a mirror substrate according to embodiments of the invention in astronomical applications or in lithography processes, such as LCD lithography and / or microlithography. BRIEF DESCRIPTION OF THE DRAWINGS

[0111] The present invention will now be explained in more detail with reference to the accompanying drawings, in which:

[0112] Figure 1 and Figure 2 An assembly including a reflector substrate and a support according to an embodiment of the present invention is shown;

[0113] Figure 3 is a view of a surface of a support according to an embodiment of the present invention; and

[0114] Figure 4The process steps for producing a mirror substrate are shown. DETAILED DESCRIPTION

[0115] Figure 1 is a schematic diagram, not drawn to scale, of an assembly 15 comprising a support 1 and a reflector substrate 20 according to one embodiment. Here, the reflector substrate 20 is designed such that the surface of the element 20 that is carried on the support 1, i.e. the carrying surface 22, has a convex curvature. In contrast, the surface 4 of the support 1 has a concave curvature to ensure the best possible support of the workpiece or glass, glass ceramic or ceramic element. Thus, the carrying surface 22 and the surface 4 have relatively complementary shapes to achieve full-surface support of the thin reflector substrate 20.

[0116] Figure 2 1 is a schematic diagram, not drawn to scale, of another embodiment of an assembly 15 consisting of a support 1 and a reflector substrate 20 carried thereon, wherein the reflector substrate 20 is designed such that a bearing surface 22 carried on the support 1 has a concave shape. In contrast, the surface 4 of the support 1 has an upwardly convex curvature to ensure the best possible support of the reflector substrate 20.

[0117] Usually, in Figure 1 and Figure 2 In the assembly 15 schematically shown but not drawn to scale, the support 1 is used to support the reflector substrate 20, which is preferably carried on the entire surface of the support 1 during its processing and / or transportation. The support 1 includes an average linear thermal expansion coefficient of less than or equal to 1*10 -6 / K, preferably less than or equal to 0.1*10 -6 / K, and most preferably less than or equal to 0.05*10 -6 / K, or even less than or equal to 0.02*10 -6 / K or even less than or equal to 0.01*10 -6 / K. The reflector substrate 20 includes a material with an average linear thermal expansion coefficient that is also less than or equal to 1*10 -6 / K, preferably less than or equal to 0.1*10 -6 / K, and most preferably less than or equal to 0.05*10 -6 / K, or even less than or equal to 0.02*10 -6 / K or even less than or equal to 0.01*10 -6 / K material. Preferably, the maximum thickness of the reflector substrate is 50 mm or less, in particular 20 mm or less, preferably 15 mm or less, more preferably 10 mm or less, and most preferably 2 mm or less. In addition, preferably, the lateral dimension of the reflector substrate 20 is at least 200 mm, and in particular can be up to 4500 mm. The reflector substrate 20 has one of the following features:

[0118] - the ratio of the lateral dimension of the reflector substrate 20 to its maximum thickness is at least 100, preferably at least 150, more preferably at least 200, and most preferably 300 or more; and / or

[0119] - The weight per unit area of ​​the reflector substrate 20 is 100 kg / m 2 or less, preferably 50kg / m 2 or less, and more preferably 30 kg / m 2 The weight per unit area is 15kg / m 2 or less is particularly preferred.

[0120] According to one embodiment of the present invention, the roughness R of the mirror surface of the reflector substrate is a At most 3.5 μm, ideally less than 1.2 μm, wherein the surface of the mirror substrate preferably has a ground surface finish. If the mirror surface of the mirror substrate has a polished surface finish, the RMS roughness is preferably less than 2 nm, most preferably less than 1 nm.

[0121] According to another embodiment of the assembly 15, the thermal expansion coefficient of the material of which the support 1 is made and the thermal expansion coefficient of the material of which the reflector substrate 20 is made differ by an absolute value of no more than 1*10 -6 / K, preferably the absolute value is not greater than 0.1*10 -6 / K, preferably the absolute value is not greater than 0.05*10 -6 / K, and the absolute value is most preferably not greater than 0.02*10 -6 / K.

[0122] Figure 3 It is shown that, for example, according to Figure 1 or Figure 2 A schematic, not-to-scale, diagram of a support member 1 according to an embodiment of the invention used in an assembly in any of the Figures.

[0123] The support 1 for supporting the mirror substrate 20 (not shown) (the mirror substrate 20 is preferably carried on the support 1 over the entire surface of the mirror substrate during its processing and / or transportation) comprises an average linear thermal expansion coefficient of less than or equal to 1*10 -6 / K, preferably less than or equal to 0.1*10 -6 / K, most preferably less than or equal to 0.05*10 -6 / K, and in certain embodiments even less than or equal to 0.02*10 -6 / K or even less than or equal to 0.01*10 -6 / K material, wherein, preferably, the lateral dimension of the support is at least 200 mm and / or at most 4500 mm.

[0124] According to one embodiment, the surface 4 of the support 1 has a curved shape, as shown in the accompanying drawings,

[0125] - wherein, preferably, the surface 4 of the support 1 approximates the envelope surface; and

[0126] - wherein, most preferably, the deviation between the support 1 and the envelope surface is:

[0127] - for a mirror substrate 20 having a lateral dimension of at least 4000 mm, the deviation is not greater than 0.5 mm, preferably not greater than 0.025 mm; and / or

[0128] - preferably, for a mirror substrate 20 having a lateral dimension of at least 2000 mm, the deviation is no greater than 0.2 mm, preferably no greater than 0.025 mm; and / or

[0129] Preferably, for a mirror substrate 20 having a lateral dimension of at least 1200 mm, the deviation is not greater than 0.1 mm, preferably not greater than 0.01 mm.

[0130] According to another embodiment of the support 1, the surface 4 of the support 1 is at least partially covered by an intermediate material 13, such as a film 13, in particular a polymer film, wherein the thickness of the intermediate material 13 (e.g. a film) is preferably at least as large as the deviation between the actual shape of the surface 4 and the envelope surface; wherein, preferably, the maximum thickness of the intermediate material 13 is at most 200 μm, preferably at most 100 μm, more preferably at most 50 μm, or most preferably not even greater than 25 μm.

[0131] In addition to the above-described curved embodiment of the support, according to a further embodiment, the support may be flat, for example for producing a flat mirror.

[0132] According to another embodiment of the support, the intermediate material 13 comprises polyvinyl chloride.

[0133] Preferably, the surface 4 of the support 1 is only partially covered by the intermediate material 13. For example, as shown here, the film (in Figure 3In the embodiment, the intermediate material 13 in the form of a small piece is applied to the surface, and in particular, the intermediate material 13 can be arranged in a regular pattern, such as a symmetrical or radially symmetrical pattern. In one embodiment, a membrane with three-fold symmetry, four-fold symmetry or multiple symmetry is proposed, and the membrane preferably has a circular or elliptical shape.

[0134] Figure 4 The method steps for producing a mirror substrate 20 are shown in several sub-images. First, the mirror substrate and the support are prepared. As shown in sub-image (a), the surface 4 of the support 1 is shaped according to a predetermined envelope surface (here concave) using a grinding tool 5 (for example a rotating grinding disc). Sub-image (b) shows the corresponding processing of the bearing surface 22 of the mirror substrate 20. Here, the bearing surface 22 is provided with a curvature that is complementary to the curvature of the surface 4. As shown in sub-image (c), once the surfaces 4, 22 have been shaped in this way, the mirror substrate 20 is placed on the support 1 and fixed. In this case, the intermediate material 13 can be used again to compensate for the remaining unequal positions in the surface and optionally also provide shock absorption during the further processing of the mirror substrate 20. For example, the mirror substrate 20 can be adhesively fixed to the support by the intermediate material 13 to prevent lateral displacement of the mirror substrate 20 and to prevent it from detaching. In the component 15 thus obtained, the functional surface 21 can then be machined out with the grinding tool 5, as shown in sub-image (d), with almost no deformation of the mirror substrate 20. Furthermore, the support 1 can be used to machine other mirror substrates, so that when a series of multiple identical mirror substrates 20 are produced, the steps according to sub-image (a) must only be performed once.

[0135] Without being limited to the examples shown, the method for producing the reflector substrate 20 according to the preferred embodiment of the present invention as described above is based on shaping the surface 4 of the support 1 and the bearing surface by material removal processing according to a predetermined shape or according to a predetermined surface profile, and the bearing surface 22 of the reflector substrate and the surface 4 of the support 1 are formed into opposite complementary shapes at least in the bearing area, and the bearing surface 22 of the reflector substrate 20 and the surface 4 of the support 1 are put together and the reflector substrate 20 is fixed to the support 1, thereby forming an assembly 15. Then, in the assembly 15, the functional surface 21 opposite to the bearing surface 22 is formed by material removal processing.

[0136] Example

[0137] Example 1

[0138] The reflector substrate is manufactured as listed in Table 1. First, a mirror blank of a specified diameter and thickness is placed on one or more layers of intermediate material located on a block of support material. The intermediate material is provided with a channel extending to the edge of the support material. The upper surface of the mirror blank is machined into a convex shape, and the mirror blank is placed together with the machined blank on a block of support material (provided with the intermediate material as described above), the surface of the support material having been ground into a concave shape that matches the convex shape of the mirror blank substrate. Then, a concave shape is formed in the mirror blank substrate by grinding, thereby reducing the thickness of the reflector substrate as required. The surface roughness obtained is listed in Table 1.

[0139] In comparative example 1, a mineral support material was used as described in DE 10 2015 112 036 A. Before the desired substrate thickness was achieved, the mirror blank was fractured in the second grinding step.

[0140] Table 1:

[0141]

[0142] *) The mirror substrate was cracked during the second grinding process

[0143] It is obvious to a person skilled in the art that the invention is not limited to the embodiment shown, but can be varied in many ways. For example, the order in which the surfaces 4 and 22 are processed is not important, for example they can also be shaped simultaneously, or in the opposite order to that shown in the sub-images, the bearing surface 22 of the reflector substrate 20 being shaped first.

[0144] List of reference numerals:

[0145] 1 Support

[0146] 5. Grinding tools

[0147] 13Intermediate Materials

[0148] 15 Components

[0149] 20 reflector substrate

[0150] 21 20 functional surfaces

[0151] 22 20 load-bearing surface

[0152] 4 The surface of the support.

Claims

1. A reflector substrate comprising a substrate having an average linear thermal expansion coefficient less than or equal to 1*10 -6 / K, preferably less than or equal to 0.1*10 -6 / K, most preferably less than or equal to 0.05*10 -6 / K material, wherein the reflector substrate has at least one of the following characteristics: - the ratio of the lateral dimension of the mirror substrate to its maximum thickness is at least 100, preferably at least 150, more preferably at least 200, and most preferably 300 or more; and - The weight per unit area of ​​the reflector substrate is 100 kg / m 2 or less, preferably 50kg / m 2 or less, more preferably 30kg / m 2 , and most preferably 15kg / m 2 or smaller; in, The reflector substrate has a roughness R a It is a mirror surface with a diameter of at most 3.5 μm, preferably less than 1.2 μm.

2. The reflector substrate according to claim 1, wherein the maximum thickness of the reflector substrate is 50 mm or less, in particular 20 mm or less, preferably 15 mm or less, more preferably 10 mm or less, and most preferably 2 mm or less, Preferably, the lateral dimension of the reflector substrate is at least 200 mm and / or at most 4500 mm, Preferably, wherein the roughness RMS of the surface is less than 2 nm, preferably less than 1 nm, wherein the surface of the reflector substrate preferably has a polished surface finish, Preferably, the reflector substrate comprises: Glass ceramics, preferably lithium aluminosilicate glass ceramics, preferably in the form of high quartz solid solution glass ceramics; and / or Ti-doped synthetic silica glass; and / or ceramics, preferably ceramics containing cordierite and / or SiC.

3. A reflector, comprising the reflector substrate according to any one of claims 1 to 2 and a high reflection layer on the mirror surface of the reflector substrate.

4. A support (1) for supporting a reflector substrate (20), preferably over its entire surface, in particular a reflector substrate (20) according to any one of claims 1 to 2, the reflector substrate (20) being carried on the support (1) during its processing and / or transportation; wherein the support comprises a mean linear thermal expansion coefficient of less than or equal to 1*10 -6 / K, preferably less than or equal to 0.1*10 -6 / K, and most preferably less than or equal to 0.05*10 -6 / K material.

5. The support according to claim 4, wherein the surface of the support carrying the reflector substrate (20) has a curved shape; in, Preferably, the surface of the support member approximates an envelope surface; and Among them, most preferably, the deviation between the support member and the envelope surface is: For a mirror substrate having a lateral dimension of at least 4000 mm, the deviation is no greater than 0.5 mm, preferably no greater than 0.025 mm; and / or Preferably, for a mirror substrate (20) having a lateral dimension of at least 2000 mm, the deviation is no greater than 0.2 mm, preferably no greater than 0.025 mm; and / or Preferably, for a reflector substrate (20) having a lateral dimension of at least 1200 mm, the deviation is no greater than 0.1 mm, preferably no greater than 0.01 mm, Preferably, said surface of said support is at least partially covered by an intermediate material (13), in particular by a film, preferably a polymer film; wherein, preferably, the thickness of the intermediate material (13) is at least as great as the deviation between the actual shape of the surface and the envelope surface; and wherein preferably, the maximum thickness of the intermediate material (13) is at most 200 μm, preferably at most 100 μm, more preferably at most 50 μm, or most preferably even not more than 25 μm, Preferably, wherein the intermediate material (13) comprises polyvinyl chloride, Preferably, the surface (4) of the support (1) is partially covered by the intermediate material (13), so that the intermediate material (13) is applied to the surface (4) in the form of spaced-apart portions, thereby defining a symmetrical, preferably radially symmetrical, preferably four-fold radially symmetrical pattern of portions of the intermediate material, wherein the portions preferably have a circular or elliptical shape.

6. An assembly comprising a support (1) and a reflector substrate (20), wherein the support (1) is used to support the reflector substrate (20) preferably over its entire surface, and the reflector substrate (20) is carried on the support (1) during its processing and / or transportation; in, The support member (1) comprises an average linear thermal expansion coefficient less than or equal to 1*10 -6 / K, preferably less than or equal to 0.1*10 -6 / K, and most preferably less than or equal to 0.05*10 -6 / K materials; Wherein, the reflector substrate includes an average linear thermal expansion coefficient less than or equal to 1*10 -6 / K, preferably less than or equal to 0.1*10 -6 / K, and most preferably less than or equal to 0.05*10 -6 / K materials; Wherein, preferably, the maximum thickness of the reflector substrate is 50 mm or less, in particular 20 mm or less, preferably 15 mm or less, more preferably 10 mm or less, and most preferably 2 mm or less; Wherein, preferably, the lateral dimension of the reflector substrate is at least 200 mm; and Wherein, the reflector substrate has at least one of the following features: - the ratio of the lateral dimension of the mirror substrate to its maximum thickness is at least 100, preferably at least 150, more preferably at least 200, and most preferably 300 or more; - The weight per unit area of ​​the reflector substrate is 100 kg / m 2 or less, preferably 50kg / m 2 or less, more preferably 30kg / m 2 , the most preferred is 15kg / m 2 or smaller; Preferably, the roughness of the mirror surface is not greater than 3.5 μm, preferably not greater than 1.2 μm.

7. The assembly according to claim 6, wherein the thermal expansion coefficient of the material of the support member and the thermal expansion coefficient of the material of the reflector substrate differ by an absolute value of no more than 1*10 -6 / K, preferably the absolute value is not greater than 0.1*10 -6 / K, preferably the absolute value is not greater than 0.05*10 -6 / K, and the absolute value is most preferably not greater than 0.02*10 -6 / K, Preferably, the surface of the support and the surface of the reflector substrate carried on the surface of the support have opposite complementary curved portions, Preferably, the reflector substrate (20) is laterally fixed on the support (4), wherein: Preferably, the reflector substrate (20) is additionally secured against detachment from the support (4).

8. A method for producing a reflector substrate (20), in particular a reflector substrate (20) according to any one of claims 1 to 2, comprising the following steps: - providing a support (1) for supporting, preferably over its entire surface, a reflector substrate (20) carried thereon; - providing a reflector substrate (20), wherein the reflector substrate (20) comprises a thermal expansion coefficient less than or equal to 1*10 -6 / K, preferably less than or equal to 0.1*10 -6 / K, and most preferably less than or equal to 0.05*10 -6 / K materials; - placing the reflector substrate (20) onto the support (1); - mechanically reprocessing the surface of the reflector substrate (20), in particular the mirror surface (21), in particular polishing, drilling, grinding or lapping; The absolute value of the difference between the thermal expansion coefficient of the material used to make the support member (1) and the thermal expansion coefficient of the material used to make the reflector substrate (20) is no more than 1*10 -6 / K, preferably the absolute value is not greater than 0.1*10 -6 / K, preferably the absolute value is not greater than 0.05*10 -6 / K, and the absolute value is most preferably not greater than 0.02*10 -6 / K.

9. The method according to claim 8, wherein the surface (4) of the support (1) and the bearing surface (22) are shaped by material removal processing according to a predetermined surface profile, wherein the bearing surface (22) of the reflector substrate (20) and the surface (4) of the support (1) are formed into opposite complementary shapes; and wherein, The bearing surface (22) of the reflector substrate (20) and the surface (4) of the support (1) are brought together and the reflector substrate (20) is fastened to the support (1) to form an assembly (15); and wherein, then, in the assembly (15), a functional surface (21) opposite to the bearing surface (22) is formed by material removal processing.

10. Use of a mirror substrate according to any one of claims 1 to 2 in astronomical applications, LCD lithography and / or microlithography.

Images