Method for smoothing a surface of a substrate

Abstract

The invention relates to a method for smoothing a surface (2) of a substrate (1) made of brittle hard material, in particular glass or glass-ceramic, comprising: smoothing the surface (2) using a brush tool (3), wherein the smoothing is carried out on an optical surface (2) of the substrate (1) until the optical surface (2) can be interferometrically measured. The brush tool (3) can have diamond-carrying filaments (4) which are preferably formed from an elastic material.

Description

[0001] Method for smoothing a surface of a substrate

[0002] Reference to related application

[0003] This application claims priority from German patent application DE102023213187.0 filed on December 21, 2023, the entire disclosure of which is incorporated by reference into this application.

[0004] Background of the invention

[0005] The invention relates to a method for smoothing a surface of a substrate made of a brittle material, in particular glass or a glass ceramic.

[0006] A brittle-hard material is defined as one with very low light absorption, such as glasses or glass-ceramics. The surfaces of such materials can be processed until they have a surface quality that makes them transparent to the transmission of light, allowing interferometric measurements to be performed on the substrate.

[0007] Currently, transparent, interferometrically measurable substrate surfaces are produced in a multi-step process: a grinding step, a fine grinding step, and a subsequent polishing step. The polishing step builds on the quality of the fine grinding step and depends on the process control of the fine grinding step, i.e., the effort and quality of the fine grinding step. During the fine grinding step, deep damage to the material is eliminated, depending on the fine grinding, the processing parameters, and the tool design.

[0008] Depending on the grinding quality or the depth of damage during the fine grinding step, a subsequent etching step to a depth of 500 μm may be required on the ground surface to eliminate the deep damage induced in the material. The inhomogeneous etching removal can result in errors regarding dimensional and shape tolerances, which may require reworking the surface in an additional fine grinding step. This fine grinding step or process introduces further deep damage, which must be kept as minimal as possible. Due to the deep damage, the production of optical surfaces is extremely complex. Furthermore, the grinding and polishing steps cannot usually be performed on a single machine.

[0009] Object of the invention

[0010] The object of the invention is to provide a method for smoothing a surface of a substrate made of a brittle material which produces the least possible deep damage.

[0011] Subject of the invention

[0012] This task is solved by a method of the type mentioned above, in which the surface of the substrate is smoothed with a brush tool.

[0013] The inventors have recognized that smoothing with a brush tool reduces the effective process forces and causes little or no deep damage to the brittle, hard substrate material. When smoothing with a brush tool, the damage caused in a previous processing step, such as a fine grinding step, can therefore be reduced by the brush tool.

[0014] Brush tools can be used to smooth contours, etched surfaces, and optical surfaces of brittle, hard materials such as glass or glass ceramics. Smoothing with a brush tool improves the surface's fine structure. The effort required for a subsequent polishing step is reduced due to the improved surface fine structure and can potentially be eliminated entirely (see below).

[0015] Filament tools in the form of brushes are generally used for deburring ceramic indexable inserts in the tool industry.

[0016] Their use for achieving cosmetic effects on surfaces is also known. However, the use of brush tools to reduce deep damage or to create transparent, interferometrically measurable surfaces on substrates made of brittle, hard materials is unknown.

[0017] In one variant, the brush tool has filaments, preferably made of an elastic material. The elastic material is typically a plastic material that flexes during the smoothing process as the brush tool is moved over the surface. However, it can also be a metallic material that flexes with a suitable filament configuration. The flexion of the filaments results in a statistically random drag of the filaments, which breaks the peaks in the surface topography, creating a smoothing effect.

[0018] In a further development of this variant, the filaments are coated with at least one material with a Mohs hardness of at least 8. In this development, the filaments typically have a material with a Mohs hardness on their surface to effect material removal and thus smooth the surface. Materials with a Mohs hardness of at least 8 can be, for example, metallic carbides, nitrides, or corundum (e.g., zirconium corundum).

[0019] In a further development, the filaments are coated with diamonds. The filaments have diamond grains on their surface, which facilitate the removal of the brittle, hard material. Diamond has a Mohs hardness of 10.

[0020] In another variant, the brush tool is positioned at a predefined distance from the surface during smoothing, preferably chosen so that the elastic filaments flex. The brush tool is subjected to a predetermined infeed while working on the surface, which, due to the elastic filaments, causes flexion and thus dragging of the diamond grains of the diamond-coated filaments. As described above, this statistically random dragging results in a smoothing effect.

[0021] In a further development of this variant, the brush tool is moved over the surface at a predefined distance along a predetermined trajectory. In this development, the contour of the surface is followed by the brush tool at a constant distance so that the brushes or filaments always have a constant contact pressure. The surface to be smoothed can be a flat surface. In this case, the previously defined feed rate of the brush tool can be maintained when the brush tool is moved over the surface. In the case of a curved surface, e.g. a free-form surface, an adjustment of the feed rate of the brush tool is typically necessary in order to maintain the constant distance from the surface. In a further variant, the brush tool is moved over the surface in a rotating, oscillating, pulsating and / or stroking or dragging motion during smoothing.The brush tool typically moves over the surface once or several times along a predetermined trajectory to achieve the desired smoothing effect. As an alternative to the variant described above, the distance of the brush tool perpendicular to the surface can be changed as it moves over the surface. For example, the brush tool can perform a pulsating or oscillating motion perpendicular to the surface.

[0022] In addition to the design of the brush tool's base body and the diamond grits, the structure and composition of the filaments can also vary depending on the surface to be processed or smoothed. The filaments can be made of plastic or metal. Process parameters such as speed, immersion depth or distance between the brush tool and the surface, as well as the trajectory, can also vary depending on the application.

[0023] Another variant involves using a cooling lubricant when smoothing the surface. In addition to its cooling effect, the cooling lubricant also binds particles that form during the surface smoothing process.

[0024] In an alternative variant, particles formed during the smoothing process are blown off the surface. In this variant, the smoothing process is carried out "dry," i.e., without the use of a cooling lubricant. The particles formed during the smoothing process are typically blown off the surface using a gas stream, e.g., an air stream.

[0025] In another variant, the surface is subjected to a fine grinding process prior to smoothing. As described above, deep damage is introduced into the surface, which is reduced by smoothing because material is removed during smoothing, but practically no additional deep damage is created. In this way, the deep damage can be reduced by the amount of material removed by the brush tool, and the fine surface structure can be improved. The amount of polishing material required on the substrate surface during subsequent polishing can also be reduced in this way. The substrate surface can be an optical or a non-optical surface.

[0026] In another variant, the surface is treated with an etching process before smoothing. As described above, the etching process can reduce the deep damage to the substrate material caused by the previous fine grinding process. As also described above, the etching process creates inhomogeneous etching material, which can cause dimensional and shape tolerances, possibly requiring a repeat fine grinding process.

[0027] Smoothing can improve the fine surface structure, so that a further fine grinding process after etching can typically be omitted.

[0028] In another variant, the smoothing is performed on an optical surface of the substrate until the optical surface can be measured interferometrically. In this variant, the smoothing is performed until a fine surface structure or a surface quality is achieved at which the optical surface of the substrate is transparent and can be measured interferometrically. In this variant, the optical surface can thus be measured directly interferometrically, without the need for a subsequent polishing step. This method can

[0029] The production of transparent, interferometrically measurable optical surfaces on substrates made of brittle material can be simplified and the processing times for producing such surfaces can be shortened.

[0030] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, with reference to the figures of the drawing, which illustrate details essential to the invention, and from the claims. The individual features can be implemented individually or in combination in a variant of the invention.

[0031] drawing

[0032] Examples of embodiments are shown in the schematic drawing and are explained in the following description.

[0033] Fig. 1a,b schematic representations of a brush tool having a cup shape, in the unloaded state and under load with deformation of the filaments, as well as

[0034] Fig. 2a, b schematic representations analogous to Fig. 1a,b for a brush tool in the form of a grinding wheel.

[0035] In the following description of the drawings, identical reference symbols are used for identical or functionally identical components.

[0036] Fig. 1a,b show a workpiece in the form of a substrate 1 made of a brittle material. In the example shown, the brittle material is quartz glass, but it can also be another type of ceramic.

[0037] For example, a flat surface 2 is designed for the passage of light or radiation. To achieve a surface quality on surface 2 that allows the passage of radiation and makes surface 2 interferometrically measurable, a manufacturing process is carried out that comprises several steps:

[0038] First, a grinding process is performed, followed by a fine grinding process of the surface 2. During the fine grinding process, deep damage is introduced into the material of the substrate 1, which is to be eliminated in a subsequent etching process. Since inhomogeneous etching removal during the etching process can lead to errors regarding dimensional and shape tolerances, the etching process is stopped in the manufacturing process described in Fig. 1a,b before the deep damage has been completely eliminated.

[0039] In order to eliminate the deep damage and improve the fine surface structure after the fine grinding and etching process, a brush tool 3 is used in a subsequent smoothing step, which in the example shown in Fig. 1a, b has a cup shape. The brush tool 3 has a plurality of elastic filaments 4 that are attached to a flat end face of a base body 5 of the brush tool 3. In one aspect of the invention, the filaments 4 consist of a plastic material. In a further aspect of the invention, the filaments 4 consist of a metallic material that bends when the filaments are suitably formed. The filaments 4 are diamond-coated, i.e., diamond grains are attached to their surfaces.Alternatively or additionally, the filaments 4 can also be coated with grains of at least one other material that is particularly hard and has a Mohs hardness of at least 8, for example, metallic carbides, nitrides, or corundum, in particular zirconium corundum. In the example shown in Fig. 1a, b, the brush tool 3 can rotate about a vertical axis of rotation 6 perpendicular to the surface 2 with the aid of a drive (not shown). The brush tool 3, which is unloaded in Fig. 1a, is brought into contact with the surface for the smoothing process.

[0040] 2 and advanced to a predetermined distance A from the surface 2. The distance A is selected such that the elastic filaments 4 bend, as can be seen in Fig. 1 b. The bending leads to a dragging of the diamond grains of the filaments 4 during the rotation of the brush tool 3. This statistically random dragging leads to a smoothing effect in which peaks in the topography of the surface 2 are broken, resulting in a smoothing of the surface 2. Due to the comparatively low process forces acting on the surface 2, practically no deep damage is caused in the material of the substrate 1 by the brush processing. Alternatively or in addition to the rotating movement of the brush tool 3, it can perform an oscillating, pulsating and / or sweeping or dragging movement.

[0041] Fig. 2a, b show a smoothing process by brushing, in which a grinding wheel is used instead of a cup-shaped brush tool 3, which is rotatable about a rotation axis 6 aligned perpendicular to the plane of the drawing. As in Fig. 1a, b, the rotating brush tool

[0042] 3 at a predetermined distance A from the surface 2, which distance is selected such that the elastic filaments 4 bend and are dragged along, which brings about the smoothing effect described above. It is understood that the brush tool 3 can also be designed in a different way than that shown in Fig. 1a, b and in Fig. 2a, b. For example, the brush tool 3 can also be designed as a spherical segment tool. The brush tool 3 is moved along over the surface 2, wherein the movement can occur once or several times, i.e. a respective position on the surface 2 can be passed over by the brush tool 3 once or several times during smoothing. The process parameters during smoothing, i.e. the speed of the brush tool 3, the immersion depth or the distance A as well as the predetermined trajectory curve can vary depending on the application.The design of the base body 5, the filaments 4, and the diamond grains, for example, their size or grain size, can also vary depending on the surface 2 to be machined. Smoothing can be performed "dry" or using a cooling lubricant. In the first case, particles created during smoothing can be blown off the surface 2.

[0043] The polishing effort required to achieve a high surface quality or a high degree of polishing in a subsequent polishing step is reduced by the smoothing effect and improved fine structure of surface 2 achieved during filament processing. Ideally, smoothing can lead to a fine surface structure that creates a transparent surface 2 suitable for interferometric measurement. In this case, a subsequent polishing step can be omitted. However, it is also possible for the smoothing step described here to be followed by a polishing step to create a transparent surface suitable for interferometric measurement. In this case, smoothing reduces the required polishing removal in the subsequent polishing step.

[0044] The substrate 1 with the surface 2, which can be measured interferometrically, can be used, for example, to produce a mirror for use in a semiconductor technology system, e.g., an EUV lithography system. In this case, a reflective coating is applied to the surface 2. The use of the substrate 1 as the base body of a transmitting optical element, e.g., in the form of semiconductor technology,

[0045] The semiconductor technology system can be, for example, a projection exposure system, a mask inspection system, or a wafer inspection system. It is understood that the smoothing process described here is not limited to the smoothing of optically used surfaces 2, but can also be applied to non-optically used surfaces of the substrate 1 in order to smooth these surfaces or their contours.

Claims

Patent claims 1 . A method for smoothing a surface (2) of a substrate (1) made of a brittle material, in particular glass or a glass ceramic, comprising: Smoothing the surface (2) with a brush tool (3), wherein the smoothing is carried out on an optical surface (2) of the substrate (1) until the optical surface (2) can be measured interferometrically.

2. Method according to claim 1, wherein the brush tool (3) has filaments (4) which are preferably formed from an elastic material.

3. Method according to claim 2, wherein the filaments (4) are coated with a material having a Mohs hardness of at least 8, which is preferably selected from the group comprising: metallic carbides, nitrides, corundum, in particular zirconium corundum.

4. Method according to claim 2 or 3, wherein the filaments (4) are diamond-coated.

5. Method according to one of the preceding claims, in which, during smoothing, the brush tool (3) is positioned at a predefined distance (A) from the surface (2), which distance is preferably selected such that the elastic filaments (4) bend.

6. The method according to claim 5, wherein the brush tool (3) is moved at the predefined distance (A) along a predetermined trajectory curve over the surface (2). the preceding claim Smoothing the brush tool (3) is moved in a rotating, oscillating, pulsating and / or stroking manner over the surface (2).

8. Method according to one of the preceding claims, in which a cooling lubricant is used when smoothing the surface (2).

9. Method according to one of claims 1 to 7, in which particles formed during smoothing are blown off the surface (2).

10. Method according to one of the preceding claims, in which the surface (2) is processed in a fine grinding process before smoothing.

11. Method according to one of the preceding claims, in which the surface (2) is processed in an etching process before smoothing.

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