Method for producing a substrate having a structured surface, and substrate having a structured surface

Abstract

In an embodiment, a method for producing a substrate having a structured surface includes providing the substrate having a substrate body and having a surface to be structured, forming an absorption layer, a first mask layer and a second mask layer on the surface to be structured, forming openings in the second mask layer in which the first mask layer is exposed, exposing the surface to be structured in a region of the openings, forming depressions in the surface to be structured in the region of the openings to form the structured surface of the substrate and removing the absorption layer from the substrate.

Claims

1. A method for producing a substrate having a structured surface, the method comprising: providing the substrate having a substrate body and having a surface to be structured; forming an absorption layer, a first mask layer and a second mask layer on the surface to be structured; forming openings in the second mask layer in which the first mask layer is exposed, wherein forming the openings in the second mask layer is carried out after forming the absorption layer, the first mask layer and the second mask layer on the surface to be structured; exposing the surface to be structured in a region of the openings; forming depressions in the surface to be structured in the region of the openings to form the structured surface of the substrate; and removing the absorption layer from the substrate.

2. The method as claimed in claim 1, wherein the surface to be structured is a surface of the substrate body.

3. The method as claimed in claim 1, wherein the surface to be structured is a surface of a layer applied to the substrate body.

4. The method as claimed in claim 1, wherein the openings in the second mask layer are formed by a lithographic exposure method, and wherein the absorption layer is designed to be absorbent with respect to radiation used in the exposure method.

5. The method as claimed in claim 1, wherein the first mask layer and the absorption layer are removed by a dry-chemical etching method in the region of the openings.

6. The method as claimed in claim 1, wherein the depressions are formed by an etching method which is selective with respect to the first mask layer.

7. The method as claimed in claim 1, wherein the second mask layer is removed prior to removing the absorption layer.

8. The method as claimed in claim 1, wherein the first mask layer is removed together with the absorption layer.

9. The method as claimed in claim 1, wherein the absorption layer is removed by a wet-chemical method.

10. A substrate comprising: a structured surface, wherein the substrate is a growth substrate for epitaxial deposition, wherein the substrate comprises a substrate body transparent in a visible spectral region, wherein the structured surface has depressions, which, at least in one direction, have a structure width of not more than 200 nm and/or a center-to-center distance of not more than 800 nm, wherein the structured surface is a structured surface of a layer arranged on the substrate body, and wherein the depressions extend completely through the layer to the substrate body so that the substrate body is exposed in a region of the depressions.

11. The substrate as claimed in claim 10, wherein the layer is a dielectric layer which is transparent to radiation in the visible spectral region.

12. The substrate as claimed in claim 10, wherein the depressions are configured as trenches that run parallel to one another with the center-to-center distance, and wherein the trenches extend in a lateral direction across an entire extent of the substrate and have the structure width perpendicular thereto.

13. A method for producing a substrate having a structured surface, the method comprising: providing the substrate having a substrate body and having a surface to be structured; forming an absorption layer, a first mask layer and a second mask layer on the surface to be structured; forming openings in the second mask layer in which the first mask layer is exposed, wherein the forming of the openings in the second mask layer is carried out after the forming of the absorption layer, the first mask layer and the second mask layer on the surface to be structured, and wherein the openings extend completely through the second mask layer; exposing the surface to be structured in a region of the openings by carrying out a first dry-chemical etching method in which the first mask layer and the absorption layer are removed in the region of the openings; forming depressions in the surface to be structured in the region of the openings to form the structured surface of the substrate by carrying out a second dry-chemical etching method subsequent to the first dry-chemical etching method; and removing the absorption layer from the substrate.

14. The method as claimed in claim 13, wherein the etching stops at the surface to be structured in the first dry-chemical etching method.

15. The method as claimed in claim 13, wherein the first dry-chemical etching method is an ICP-RIE (reactive ion etching with inductively coupled plasma) method based on fluorine chemistry, and wherein the second dry-chemical etching method is a dry-chemical etching method based on chlorine chemistry.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further configurations and benefits will be apparent from the description of the working examples that follows, in conjunction with the figures.

(2) FIGS. 1A to 1F show a working example of a method of producing a substrate with a structured surface using intermediate steps that are each represented in a schematic section view, with FIG. 1F showing a working example of a completed substrate;

(3) FIGS. 2A and 2B show a working example of a method of producing a substrate with a structured surface using intermediate steps that are each represented in a schematic section view, with FIG. 2B showing a working example of a completed substrate.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(4) Elements that are the same, of the same type or have the same effect are given the same reference numerals in the figures.

(5) The figures are each schematic diagrams and therefore not necessarily true to scale. Instead, comparatively small elements and especially layer thicknesses can be shown in excessively large size for clarity.

(6) In the working example shown in FIGS. 1A to 1F, only part of the region of the substrate to be produced is shown, in which a depression is formed. The substrate may have a multitude of such depressions.

(7) In the working example shown in FIGS. 1A to 1F, a substrate 1 with a surface 110 to be structured is provided. The substrate 1 has a substrate body 10 and a layer disposed atop the substrate body 15, for example a dielectric layer. The layer 15 is disposed atop a surface 100 of the substrate body 10 and covers it, especially over the full area.

(8) In the figures, for better representability, only the upper portion of the substrate body 10 is shown in the region of the surface 100 of the substrate body. The substrate body 10 is the element of the substrate 1 that has the greatest thickness, i.e. the greatest vertical extent in a direction perpendicular to the surface 110 to be structured. For example, the substrate body 10 has a thickness of at least 100 m or at least 200 m and/or at most 2 mm or at most 1 mm.

(9) A suitable substrate body 10 is, for example, sapphire or gallium nitride. However, it is also possible to employ a different material, for example gallium phosphide.

(10) A thickness of the layer 15 is, for example, between 10 and 200 nm inclusive.

(11) A dielectric material, for example, is suitable for layer 15, for instance an oxide such as silicon oxide or aluminum oxide, or a nitride, for instance silicon nitride.

(12) An absorption layer 2, a first mask layer 3 and a second mask layer 4 are applied to the surface 110 to be structured.

(13) A suitable material for the absorption layer 2 is, for example, one which absorbs in the visible spectral region, for instance a semiconductor material having a comparatively small bandgap, for example germanium or silicon.

(14) A thickness of the absorption layer is, for example, between 50 nm and 300 nm inclusive, for example 150 nm.

(15) A suitable material for the first mask layer is, for example, a transparent conductive oxide (TCO) such as indium tin oxide (ITO). A layer thickness of the first mask layer is, for example, between 15 nm and 150 nm inclusive. A suitable material for the second mask layer 4 is, for example, a photoresist.

(16) Formed in the second mask layer 4, as shown in FIG. 1B, are openings 40, in which the first mask layer 3 is exposed. This purpose is suitably served, for example, by a lithography method, followed by wet-chemical etching of the second mask layer 4. The openings 40 narrow toward the substrate 1, such that a first extent 41 on a side of the second mask layer 4 remote from the substrate 1 is greater than a second extent 42 on a side facing the substrate 1. For example, the second extent 42 may be at most half as great as the first extent 41. For example, a second extent 42 of 190 nm was achieved in the case of a first extent 41 of 460 nm.

(17) The first mask layer 3 and the second mask layer 4 are matched here to one another such that the wet-chemical etching stops at the second mask layer 3.

(18) In the step shown in FIG. 1C, the second mask layer 4 serves as an etching mask for a dry-chemical etching method in which the surface 110 to be structured is exposed. Further openings 30 are formed here, which extend through the first mask layer 3 and the absorption layer 2. The dry-chemical etching method which is used for the forming of the further openings 30 is selective with respect to the material at the surface 110 to be structured, i.e. the material of layer 15, such that the etching stops at the surface 110 to be structured. This purpose is served, for example, by an ICP-RIE method based on fluorine chemistry, which etches ITO, for example, as the first mask layer, but not SiO2 as layer 15 of the surface 110 to be structured. The material at the surface 110 to be structured and of the first mask layer 3 are thus matched to one another such that the first mask layer 3 is etched efficiently without attacking the surface 110 to be structured.

(19) The further openings 30 narrow toward the substrate 1. Subsequently, as shown in FIG. 1D, depressions 17 are formed in the surface 110 to be structured. As a result, the structured surface 11 is formed. The depressions 17 can extend right through the layer 15, such that the substrate body 10 is exposed in the depressions 17.

(20) A dry-chemical etching method which is employed with preference for the forming of the depressions 17 is selective with respect to the first mask layer 3. This can avoid any increase in the width of the further openings 30 at the level of the first mask layer 3 during the etching operation. This could lead to broadening of the structure to be produced.

(21) For example, a dry-chemical etching method based on chlorine chemistry is suitable for this purpose when ITO is used for the first mask layer 3.

(22) Subsequently, the second mask layer 4 is removed (FIG. 1E), for example by wet-chemical etching. Thereafter, the absorption layer 2 is removed by a wet-chemical etching method. This also lifts off the first mask layer 3 disposed atop the absorption layer 2. The first mask layer 3 is thus removed without having to attack the material of the first mask layer 3 itself by means of the wet-chemical etching method for the etching of the absorption layer 2.

(23) Nor is the structured surface 11 attacked by this method, and so the structuring of the structured surface 11 is at least not significantly altered, if at all.

(24) Finally, a cleaning operation can be conducted in order to remove organic or nonorganic residues from the structured surface 11.

(25) The completed substrate 1 shown in FIG. 1F thus has a structured surface 11 and is prepared for epitaxial deposition of semiconductor material on the structured surface 11. This is also referred to as epi-ready. The growth may proceed from the sites on the substrate body 10 that are exposed in the depressions 17.

(26) The depressions 17 in the structured surface 11 have, for example, at least in one lateral direction, a structure width 171 of not more than 200 mm (cf. FIG. 2B) and/or a center-to-center distance 172 of not more than 800 nm.

(27) The structure width 171 of the depressions 17 produced is not significantly less than the first extent 41 of the second mask layer 4 on the side remote from the substrate 1. The structure width is thus not restricted by the minimum first extent 41 achievable. By virtue of the production process described, it is thus possible to achieve structure widths which, through direct etching of the surface 110 to be structured, would not be achievable directly by a method suitable for mass production.

(28) For example, the structured surface 11 has a multitude of trenches that run parallel to one another at the center-to-center distance 172, which extend in a lateral direction across the entire extent of the substrate 1 and have the structure width 171 perpendicular thereto. However, the depressions 17 may also have different shapes, especially also shapes that are surrounded around the entire circumference, for example round or polygonal basic shapes. In addition, it is also possible to form various structures atop the substrate 1.

(29) For example, the specific material combination that follows has been found to be suitable: sapphire for the substrate body 10, silicon oxide having a layer thickness of 80 nm for layer 15, an absorption layer 2 having a layer thickness of 150 nm of germanium, a 50 nm-thick first mask layer 3 of ITO, and a photoresist for the second mask layer 4. However, the materials and layer thicknesses may be varied within wide limits.

(30) The working example shown in FIGS. 2A and 2B differs from the working example described in connection with FIGS. 1A to 1F in that the surface 110 to be structured is formed by a surface 100 of the substrate body 10. The absorption layer 2 is thus deposited directly on the substrate body 10.

(31) The forming of the openings 40 in the second mask layer 4 and the forming of the further openings 30 in the first mask layer 3 for exposure of the surface 110 to be structured can be affected as described in connection with FIGS. 1B to 1D. The forming of the depressions 17 can in principle be affected as described in connection with FIG. 1E, with formation of the depressions directly in the substrate body 10. The depressions 17 thus extend into the substrate body 10. The subsequent production steps, for instance the removing of the absorption layer 2 and optionally cleaning of the substrate 1, can likewise be conducted analogously to the previous working example.

(32) By means of the absorption layer 2, an automatic optical recognition which is favorable for mass production is simplified for the structuring of transparent substrates 1 as well. In addition, the reliability of the lithography method can be increased, for example on account of simplified focusability. For instance, especially in conjunction with the multistage structuring method described using at least two mask layers, it is possible to produce growth substrates with a structure width reliably and in a manner suitable for mass production with small structure sizes and/or center-to-center distances.

(33) The invention is not limited by the description with reference to the working examples. Instead, the invention encompasses every new feature and every combination of features, which especially includes any combination of features in the claims, even if this feature or this combination itself is not specified explicitly in the claims or the working examples.