Diamond-coated AIN substrate and method for manufacturing it

Abstract

This invention provides a method for coating the surface of an aluminum nitride substrate with a diamond layer using a CVD reactor. [Solution] The present invention relates to a device having a substrate 2 made of aluminum nitride, which has an upper surface 4 and a lower surface 6 facing the upper surface 4, and the upper surface 4 is coated with a diamond layer 8, wherein the coated area of ​​the lower surface 6 has a carbon-containing coating 10 containing at least 50% sp2 hybridized carbon, the free area 12 of the lower surface 6 has a carbon-containing coating 10 that is thinner than the coated area, and regardless of the thickness profile of the carbon-containing coating in the coated area of ​​the lower surface, the thickness of the coating 10 in the free area 12 is smaller than in the portion of the coated area that directly surrounds or directly adjacent to the free area 12, and the free area 12 forms at most 10% of the lower surface 6 of the substrate 2.

Description

Technical Field

[0001] The present invention relates to an apparatus having a substrate made of aluminum nitride (AlN) that has an upper surface and a lower surface facing the upper surface, and the surface is coated with a diamond layer. Further, the present invention relates to a method of coating the surface of a substrate made of aluminum nitride with a diamond layer in a CVD reactor.

Background Art

[0002] From the prior art, it is known to apply a diamond layer to a substrate in order to be able to utilize the favorable properties of diamond. For example, in order to utilize that the diamond layer is chemically inert and very stable mechanically and thermally, electrodes for an electrochemical cell are coated with a doped diamond layer, and this doping is necessary to increase the conductivity of the diamond layer which would otherwise be electrically insulating. In another application, the mechanical hardness and durability of diamond are utilized.

[0003] For example, CVD reactors are often used to coat a diamond layer onto a substrate such as a silicon single crystal. CVD stands for "chemical vapor deposition." The CVD method is a known prior art technique. The carbon required for the formation of the diamond layer is obtained from methane introduced into the reactor. The challenge lies in selecting process parameters so that the diamond layer is actually deposited and no other possible carbon layers are deposited. For example, when a silicon single crystal is used as the substrate, the adhesion of the deposited diamond layer is usually high enough to use the coating substrate for each application. A substrate coated on both sides with a diamond layer, intended as an electrode for electrochemical applications, is known from German Patent Application Publication No. 102021110587A1. The type and quality of the deposited diamond layer depend on a set of parameters, which should be adjusted as precisely as possible. This is evident, for example, regarding temperature in German Patent Application Publication No. 69629980T.

[0004] In the prior art, attempts have been made to coat a substrate made from aluminum nitride, i.e., ceramic, with a diamond layer, and to apply the CVD method in this process. This can be seen, for example, in German Patent Application Publication No. 19710202A1 and Chinese Patent Application Publication No. 113755819A. However, this leads to poorer-than-expected adhesion of the diamond layer deposited on the substrate. In the sense of the present invention, an aluminum nitride substrate is an aluminum nitride ceramic that may additionally contain additives used in the manufacture of ceramics to affect the chemical, thermal, and / or mechanical properties of the ceramic, which is often subjected to a sintering process.

[0005] Thus, coating aluminum nitride ceramics has proven difficult for several reasons. Metallic aluminum residue, i.e., a relatively large area of ​​metallic aluminum, can be problematic, and under the high temperatures generated during CVD coating, this can melt. Aluminum has a melting point of approximately 660°C. CVD reactors reach temperatures of up to 900°C, causing the metallic aluminum to melt. Where metallic aluminum is present on the surface, the substrate liquefies, potentially preventing the formation of a diamond layer. Furthermore, due to the high vapor pressure of aluminum, a significant proportion of the aluminum transitions to a gaseous state, thus severely contaminating not only the coating deposited by the gaseous atmosphere in the CVD reactor but also the reactor itself. As a result, the surface becomes unusable only after a time-consuming, costly, and expensive thorough cleaning.

[0006] Another problem can arise when the additives used in ceramics, such as Y2O3, are often unknown. Not only their composition, but also their melting point, boiling point, or gas pressure are often unknown, making it almost impossible to predict how the additives will behave when coating the surface of a substrate, whether the coating is durable, or even suitable.

[0007] Another difficulty lies in the fact that the aluminum nitride substrate and the diamond layer to be coated have very different crystallographic properties. Aluminum nitride is a polycrystalline ceramic, and aluminum nitride crystals have an HDP lattice. The abbreviation HDP stands for "hexagonal close-packed." In contrast, the diamond layer grows in a cubic crystal lattice, and the (1 1 1) plane of this cubic lattice has a high degree of incompatibility with the HGP lattice. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] German Patent Application Publication No. 102021110587A1 Specification [Patent Document 2] German Patent Application Publication No. 69629980T [Patent Document 3] German Patent Application Publication No. 19710202A1 [Patent Document 4] Chinese Patent Application Publication No. 113755819A Specification [Overview of the Initiative]

[0009] The object of the present invention is to improve the apparatus described in the premise of claim 1 and propose a method for coating the surface of an aluminum nitride substrate with a diamond layer using a CVD reactor.

[0010] The present invention solves the given problem with a device having a substrate made of aluminum nitride, having an upper surface and a lower surface facing the upper surface, the upper surface being coated with a diamond layer, wherein the coated area of ​​the lower surface has a carbon-containing coating containing at least 50% sp2 hybridized carbon, the free area of ​​the lower surface has a carbon-containing coating that is thinner than the coated area, and regardless of the thickness profile of the carbon-containing coating in the coated area of ​​the lower surface, the thickness of the coating in the free area is smaller than in the portion of the coated area that directly surrounds or directly adjacent to the free area, and the free area forms 10% of the lower surface of the substrate.

[0011] The carbon-containing coating on the underside of the substrate does not necessarily have a constant thickness. Preferably, the thickness of the coating in the coated area decreases as the distance from the edge of the underside of the substrate increases. The thickness of the coating may be constant in the coated area. The carbon-containing coating may also be present in the free area on the underside of the substrate. Therefore, the concept of a "free area" should not be understood as a region where no coating should be present. However, any coating present in such a free area has a smaller thickness than the carbon-containing coating in the coated area on the underside of the substrate. Regardless of the thickness profile of the carbon-containing coating in the coated area on the underside, the thickness of the coating deposited in situ in the free area on the underside is smaller than the thickness in the portion of the coated area that directly surrounds or is directly adjacent to the free area. This does not necessarily mean that the thickness of the carbon-containing coating is greater in every location of the coated area than in every location of the free area, but this is one preferred embodiment. It is entirely possible for the thickness of the coating in the free area to be greater than the thickness at one location of the coated area. This is possible, for example, when the free region is located near the edge of the lower surface of the substrate, and the corresponding part of the coating region is far from the edge of the lower surface.

[0012] The carbon-containing coating preferably has a stepped portion at the boundary between the coated area and the free area. In this case, the stepped portion is a region in which the derivative of the thickness at each location is clearly larger than that at other locations on the lower surface.

[0013] It is preferable that the free region does not have a carbon-containing coating. In that case, the coating thickness in this region is zero.

[0014] Preferably, the carbon-containing coating on the lower surface extends to the side surface of the substrate connecting the upper surface to the lower surface. Preferably, the thickness of the carbon-containing coating on the side surface of the substrate decreases from the upper surface toward the lower surface of the substrate.

[0015] The carbon-containing coating on the underside of the substrate, and optionally on the sides of the substrate, is preferably applied in the same coating process as the diamond layer on the top surface of the substrate. To apply the carbon-containing coating to the underside of the substrate, the entire underside must not rest on the sample stage, but must be able to come into contact with a gas atmosphere, for example, inside a coating reactor such as a CVD reactor. To achieve this, it is preferable to support the substrate on one or more supports, thereby creating an intermediate space between the underside of the substrate and the sample stage that allows the gas atmosphere to enter. The underside of the substrate typically has a temperature that is often not sufficient to precipitate the diamond layer, but is sufficiently high to form another carbon-containing material.

[0016] Where the underside of the substrate rests on at least one support, the gas atmosphere does not come into contact with the underside of the substrate, or comes into contact with it only minimally, resulting in at least one free region where the underside of the substrate has only a relatively thin carbon-containing coating, or no carbon-containing coating at all.

[0017] The fundamental finding of this invention is that if a carbon-containing coating is present in a coating region on the lower surface of the substrate, and there is at least one free region where there is only a relatively thin coating or no such coating at all, the adhesion of the diamond layer to the upper surface of the substrate is improved.

[0018] The free region is preferably annular, and more preferably annular or polygonal. The free region is preferably formed from a plurality of separate subregions. Each of these subregions may be circular, elliptical, or polygonal, or may have other shapes. Different subregions may have the same shape and / or the same size. Different subregions may have different shapes and / or different sizes. In one preferred embodiment, some of these subregions are partially annular, jointly forming an annular free region with interruptions, and preferably an annular or polygonal free region with interruptions.

[0019] In a preferred embodiment, the free region forms at most 6%, and especially preferably at most 3%, of the lower surface of the substrate.

[0020] The upper surface of the substrate preferably has at least one structural element, particularly at least one raised portion and / or at least one recess. The lower surface of the substrate preferably has at least one structural element, particularly a raised portion and / or at least one recess. Such raised portions or recesses preferably have a height or depth of at least 1 mm, preferably at least 2 mm, and at most 10 mm, preferably at most 8 mm.

[0021] It is preferable that at least one structural element on the lower surface is located in a region of the lower surface that has only a relatively thin carbon-containing coating or does not have a carbon-containing coating. It is especially preferable that all structural elements on the lower surface are located in a region of the lower surface that has only a relatively thin carbon-containing coating or does not have a carbon-containing coating.

[0022] At least one structural element present on the lower or upper surface of the substrate is preferably a recess into which an electronic component such as a sensor is to be inserted in a subsequent manufacturing process. As an alternative or addition thereto, at least one structural element is a notch or groove into which an electrical or signal line is to be inserted in a subsequent method step. Therefore, it is preferred that these structural elements are not covered with a carbon-containing coating.

[0023] The diamond coating on the upper surface of the substrate preferably contains less than 5%, preferably less than 3%, particularly preferably less than 1% of sp2 hybridized carbon.

[0024] The carbon-containing coating has a proportion of sp2 hybridized carbon. The carbon-containing coating on the lower surface of the substrate preferably contains at least 70%, particularly preferably at least 90% of sp2 hybridized carbon. The carbon-containing coating may be partially a diamond coating and / or a diamond-like coating (DLC). The proportion of the carbon-containing coating that is less than 100% is preferably a diamond coating and / or a diamond-like coating.

[0025] The device preferably has sodium carbonitride (empirical formula AlCN) between the aluminum nitride of the substrate and the diamond layer on the upper surface of the substrate.

[0026] The diamond layer on the upper surface of the substrate is preferably doped, and the doping preferably contains boron and / or phosphorus and / or nitrogen.

[0027] In one preferred embodiment, the diamond layer has a uniform thickness. This applies, for example, when the diamond layer is at most 2 μm, preferably at most 1 μm, particularly preferably at most 0.2 μm thicker at the thickest point of the diamond layer than at the thinnest point of the diamond layer.

[0028] In a preferred embodiment, the lower surface of the substrate has a diamond coating, with a carbon-containing coating positioned above and / or below it. This embodiment can be manufactured, for example, by a first coating step in which a diamond layer is deposited on the upper surface of the substrate and simultaneously a carbon-containing coating is deposited on the lower surface of the substrate. In this case, the substrate is turned over so that the diamond-coated upper surface is facing downwards. A second coating step is then performed in this position, during which a diamond layer is applied to the lower surface. When the lower surface is coated with diamond, the thickness of the carbon-containing coating previously deposited on the lower surface is reduced by the diamond coating.

[0029] Alternatively, in the first coating process, the underside of the substrate can also be coated with a diamond layer. For this purpose, the substrate is loaded into the reactor with the underside facing upwards. After the diamond layer is applied to the underside of the substrate, the substrate is turned over so that the top surface faces upwards and is coated again. In this second coating process, a diamond layer is formed on the top surface of the substrate, and at the same time, a carbon-containing coating is formed on the underside of the substrate. Therefore, this is deposited on top of the diamond layer, i.e., it exists on top of the diamond layer.

[0030] This invention solves the problems presented by a method of coating the surface of a substrate made of aluminum nitride with a diamond layer using a CVD reactor, and the following: a. A process in which the surface outside the reactor is etched with an etching agent, thereby creating a prepared surface, b. A process in which diamond particles are seeded onto the prepared surface, c. A substrate having a seeded surface is positioned on a sample stage, and at this time the substrate is supported on at least one support part; d. The process of positioning the sample stage together with the substrate in the reactor, e. A process in which the reactor and substrate are heated to the operating temperature, f. A step in which a diamond layer is deposited on the surface and a carbon-containing coating containing at least 50% sp2 hybridized carbon is deposited on the underside of the substrate, Includes.

[0031] In the first step, the surface to be coated with the diamond layer is etched outside the reactor. At this time, a chemical etching agent is used, for example, to remove impurities from the surface. It is preferable that at least 90%, preferably at least 95%, and especially preferably 100%, of the contaminants present on the surface, particularly organic and / or metallic contamination of the surface, are removed. The surface thus treated is prepared for seeding and is therefore referred to as the prepared surface.

[0032] The prepared surface is seeded with diamond particles. Seeding the surface of a substrate is fundamentally known from the prior art. For this purpose, a suspension containing, for example, microcrystalline diamond particles and / or nanocrystalline diamond particles is prepared. This suspension is applied to the surface to be coated with a diamond layer.

[0033] After seeding, the substrate is positioned on the sample stage. The sample stage, along with the positioned substrate, is then positioned in the reactor. Accurate positioning at this stage is of great importance. To minimize problems caused by potentially present metals such as aluminum or other additives, it is preferable that the diamond layer for surface coating grows and precipitates as quickly as possible. For this reason, it is preferable that as wide an area of ​​the surface as possible, and especially preferably the entire surface, has a temperature sufficient for the coating and deposition of the diamond layer, which is reached in the CVD reactor by the filament heated by the electric current. Therefore, it is of great importance to align the substrate with the filament so that as much of the generated heat as possible can be received by as wide an area of ​​the surface as possible.

[0034] Next, the reactor and the substrate placed inside it are heated to an operating temperature, which may be, for example, 900°C. Then, the diamond layer is deposited on the surface of the substrate.

[0035] Preferably, the diamond layer is deposited on the underside of the substrate in a separate process, and it is preferable that the substrate is turned over beforehand.

[0036] In preferred embodiments, the etching agent is or contains phosphoric acid (H3PO4). This is relatively low-cost and clearly a preferred choice in terms of operational safety over etching agents such as hydrogen fluoride (HF), also known as hydrochloric acid and known in the prior art as an etching agent.

[0037] Seeding is preferably performed before the substrate is positioned within the reactor.

[0038] The substrate is preferably supported on multiple support structures and positioned on the sample stage. That is, rather than resting entirely on the sample stage as is known from the prior art, the substrate is supported on support structures that cause a region of the substrate's underside to come into contact with the gas atmosphere inside the reactor. This underside region is coated with a carbon-containing coating, while the upper surface is coated with a diamond layer.

[0039] This significantly reduces thermal contact with other objects, particularly the sample stage, resulting in less heat being transferred from the substrate to other objects, especially the sample stage. Consequently, the surface of the aluminum nitride substrate facing away from the support reaches the temperature necessary for diamond layer deposition more quickly, for a longer period, and more uniformly, preferably over a wider area. This results in the ability to coat larger substrates and wider surfaces, and on the other hand, the deposition of the diamond layer more rapidly, resulting in the formation of a closed film on the surface of the aluminum nitride substrate, thereby resolving problems caused by unknown additives in metallic aluminum and / or aluminum nitride ceramics as quickly as possible. After the diamond layer forms a closed film on the substrate surface, this diamond layer is further coated and grown in subsequent coating processes. Substrates, additives, or metallic phases no longer interfere with, hinder, and / or affect the coating.

[0040] It is preferable that there are at least three support points on which the substrate is supported. The positions of the three or more support points preferably form an isosceles triangle or polygon, which is configured to be large enough on the one hand to ensure that the substrate is securely supported on the support points, and as small as possible on the other hand to position the contact area between the support points and the back surface of the substrate as close as possible to the center of the substrate. The support points may be manufactured to be positioned at the edges of the bottom surface. It is preferable that the support points contact the edges of the substrate where the bottom surface of the substrate is in contact with the sides of the substrate. The support points may be attached to at least one side of the substrate and preferably manufactured to be fixedly bonded to the substrate during coating. In this case, the free area of ​​the bottom surface is formed by the shadow of the coating of the support points.

[0041] It is preferable that the base material has extensions that protrude from the edges of the lower surface of the base material. In this case, it is preferable to place at least some, preferably all, of the support parts on these extensions.

[0042] The central region of the substrate surface is heated most intensely by the filament, so heat can dissipate most quickly here without the temperature dropping below the temperature required for the deposition of the diamond layer. It is preferable to have more than three, for example, at least six, preferably at least ten, and especially preferably at least twenty, supports on which the substrate is supported. The more supports there are, the more evenly they can be distributed, thereby reducing the spacing between two supports, which reduces the bending of the substrate and also reduces the mechanical stress that may be caused by support at fewer points.

[0043] The surrounding member is preferably positioned on the sample stage, thereby surrounding the substrate at least partially, but preferably entirely, in a plane parallel to the sample stage. This addresses the phenomenon where the edge regions of the substrate are disproportionately heavily coated in the absence of the surrounding member. The surrounding member preferably has an upper surface that ends on the same plane as the edge of the substrate's surface. The surface edge is preferably the edge where the surface and side of the substrate meet. A gap exists between the edge of the substrate's surface and the surrounding member, preferably a circumferential gap, which is formed as small as possible to enhance the effect of the surrounding member on the diamond layer to be deposited. This gap is preferably at most 2 mm wide, preferably at most 1 mm wide. The surface of the substrate to be coated with the diamond layer is preferably flat, i.e., it forms a portion of a flat surface. In this case, the upper surface of the surrounding member is also preferably extended in that plane.

[0044] In a preferred embodiment of this method, the atmosphere inside the reactor contains a small amount of methane during heating, such that the atmosphere etches the prepared surface. This ensures that, on the one hand, carbon, and consequently diamond, are not deposited on the surface to be coated during this process. On the other hand, surface impurities are prevented by the etching action of atomic hydrogen in the atmosphere, for example, by reactions with components or substances contained in the atmosphere.

[0045] The surface of the substrate preferably extends for at least 15 cm, preferably at least 20 cm, and especially preferably at least 25 cm, in at least one direction. The substrate preferably extends no more than 1 m in that direction.

[0046] Next, embodiments of the present invention will be described in detail with reference to the attached drawings. The drawings are as follows: [Brief explanation of the drawing]

[0047] [Figure 1] A schematic cross-sectional view of an apparatus based on one embodiment of the present invention is shown. [Figure 2] A schematic diagram of the lower surface of an apparatus based on another embodiment of the present invention is shown. [Modes for carrying out the invention]

[0048] Figure 1 shows a schematic cross-sectional view of an apparatus based on one embodiment of the present invention. This apparatus comprises a substrate 2 made of aluminum nitride, having an upper surface 4 and a lower surface 6. The upper surface 4 has a diamond layer 8 that completely covers the upper surface 4 of the substrate 2 in the illustrated embodiment. This is preferred in all embodiments described. The lower surface 6 has a carbon-containing coating 10, however, this does not cover the entire lower surface 6, but only the coated area of ​​the lower surface. The carbon-containing coating has a gap that forms a free area 12 of the lower surface 6. The lower surface 6 of the substrate 2 has a structural element 14 in the form of a recess. This structural element 14 is in the free area 12 of the lower surface 6 and is therefore not covered by the carbon-containing coating 10. This is preferred but not essential. It is also possible that the structural element is located in the coated area of ​​the lower surface 6 and is accordingly covered by the carbon-containing coating.

[0049] Figure 2 shows a schematic diagram of the lower surface 6 of a device based on another embodiment of the present invention. The lower surface has four rectangular sub-regions 16. Naturally, other geometric shapes are also possible. The sub-regions 16 jointly form the free region 12 of the lower surface 6. Furthermore, a structural element 14 having a recessed shape is schematically shown within the sub-region 16 shown in the upper right of Figure 2. [Explanation of Symbols]

[0050] 2 Base material 4 Top side 6 Bottom side 8 Diamond Layer 10. Carbon-containing coating 12 Free area 14 Structural elements 16 subregion

Claims

1. An apparatus having a substrate (2) made of aluminum nitride, having an upper surface (4) and a lower surface (6) facing the upper surface (4), wherein the upper surface (4) is coated with a diamond layer (8), wherein the coated area of ​​the lower surface (6) has a carbon-containing coating (10) containing at least 50% sp2 hybridized carbon, the free area (12) of the lower surface (6) has a carbon-containing coating (10) that is thinner than the coated area, and regardless of the thickness profile of the carbon-containing coating in the coated area of ​​the lower surface, the thickness of the coating (10) in the free area (12) is smaller than in the portion of the coated area that directly surrounds or directly adjacent to the free area (12), and the free area (12) forms at most 10% of the lower surface (6) of the substrate (2).

2. The apparatus according to claim 1, characterized in that the free region (12) extends in an annular shape.

3. The apparatus according to claim 1, characterized in that the free region (12) is composed of a plurality of mutually separated subregions (16).

4. The apparatus according to any one of claims 1 to 3, characterized in that the free region (12) forms at least 6%, and particularly preferably at least 3%, of the lower surface (6) of the substrate (2).

5. The apparatus according to any one of claims 1 to 4, characterized in that the upper surface (4) of the substrate (2) has at least one structural element (14), in particular at least one protrusion and / or at least one recess.

6. The apparatus according to any one of claims 1 to 5, characterized in that the lower surface (6) of the base material (2) has at least one structural element (14), particularly a raised portion and / or at least one recess.

7. The apparatus according to claim 6, characterized in that at least one of the structural elements (14) of the lower surface (6) is located in the free region (12) of the lower surface (6).

8. The apparatus according to any one of claims 1 to 7, characterized in that the diamond layer (8) on the upper surface (4) of the substrate (2) contains less than 5%, preferably less than 3%, and particularly preferably less than 1% of sp2 hybridized carbon.

9. The apparatus according to any one of claims 1 to 8, characterized in that the carbon-containing coating (10) on the lower surface (6) of the substrate (2) contains at least 70%, and particularly preferably at least 90%, of sp2 hybridized carbon.

10. The apparatus according to any one of claims 1 to 9, characterized in that the diamond layer (8) is doped, and the doping preferably includes boron and / or phosphorus and / or nitrogen.

11. The apparatus according to any one of claims 1 to 10, characterized in that the diamond layer (8) is at its thickest point that is at a maximum of 2 μm, preferably at a maximum of 1 μm, and particularly preferably at a maximum of 0.2 μm, thicker than the thinnest point of the diamond layer.

12. The apparatus according to any one of claims 1 to 11, characterized in that the lower surface (6) of the substrate (2) also has a diamond coating, and a carbon-containing coating is disposed above and / or below it.

13. In a method for coating the upper surface (4) of a substrate (2) made of aluminum nitride with a diamond layer (8) using a CVD reactor, the method comprises the following steps, namely: a. A step in which the upper surface (4) is etched with an etching agent outside the CVD reactor, thereby creating the prepared upper surface (4), b. A step of seeding diamond particles onto the prepared upper surface (4), c. The substrate having the seeded upper surface (4) is positioned on the sample stage, and at this time the substrate is supported on at least one support portion; d. A step in which the sample stage is positioned together with the substrate (2) in the CVD reactor, e. A step in which the CVD reactor and the substrate (2) are heated to an operating temperature, f. A step in which a diamond layer (8) is deposited on the upper surface (4), and a carbon-containing coating (10) containing at least 50% sp2 hybridized carbon is deposited on the lower surface (6) of the substrate (2), Methods that include...

14. The method according to claim 13, further characterized in that a diamond layer (8) is deposited on the lower surface (6) of the substrate (2) in another step, and the substrate (2) is preferably turned over beforehand.

Images