EP-4741527-A1 - DIAMOND COATED AIN SUBSTRATE AND METHOD OF MAKING

Abstract

The invention relates to a device with a substrate (2) made of aluminum nitride, which has a top surface (4) and a bottom surface (6) opposite the top surface (4), wherein the top surface (4) is coated with a diamond layer (8), characterized in that a coated area of the bottom surface (6) has a carbon-containing coating (10) containing at least 50% sp2-configured carbon, and a free area (12) of the bottom surface (6) has a thinner carbon-containing coating (10) than the coated area, wherein, regardless of the thickness profile of the carbon-containing coating in the coated area of the bottom surface, the thickness of the coating (10) in the free area (12) is less than in the part of the coated area directly surrounding or directly adjacent to this free area (12), wherein the free area (12) forms at most 10% of the bottom surface (6) of the substrate (2).

Inventors

• Cymann, Benjamin
• Graßl, Tobias
• Mathiak, Dirk
• Matthée, Thorsten
• NEUBER, Rieke

Assignees

• CONDIAS GMBH

Dates

Publication Date

20260513

Application Date

20251017

Claims (14)

1. Device with a substrate (2) made of aluminum nitride, having a top surface (4) and a bottom surface (6) opposite the top surface (4), wherein the top surface (4) is coated with a diamond layer (8), characterized in that a coated area of the bottom surface (6) has a carbon-containing coating (10) containing at least 50% sp2-configured carbon, and a free area (12) of the bottom surface (6) has a thinner carbon-containing coating (10) than the coated area, wherein, regardless of the thickness profile of the carbon-containing coating in the coated area of the bottom surface, the thickness of the coating (10) in the free area (12) is less than in the part of the coated area directly surrounding or directly adjacent to this free area (12), wherein the free area (12) forms at most 10% of the bottom surface (6) of the substrate (2).
2. Device according to one of the preceding claims, characterized in that the free area (12) extends in a ring shape.
3. Device according to claim 1, characterized in that the free area (12) is formed from a plurality of separate sub-areas (16).
4. Device according to one of the preceding claims, characterized in that the free area (12) forms at most 6%, particularly preferably at most 3% of the underside (6) of the substrate (2).
5. Device according to one of the preceding claims, characterized in that the upper surface (4) of the substrate (2) has at least one structural element (14), in particular at least one raised area and/or at least one recessed area.
6. Device according to one of the preceding claims, characterized in that the underside (6) of the substrate (2) has at least one structural element (14), in particular a raised area and/or at least one recessed area.
7. Device according to claim 6, characterized in that the at least one structural element (14) of the underside (6) is located in the free area (12) of the underside (6).
8. Device according to one of the preceding claims, characterized in that the diamond coating (8) on the top side (4) of the substrate (2) contains less than 5%, preferably less than 3%, particularly preferably less than 1% sp2-configured carbon.
9. Device according to one of the preceding claims, characterized in that the carbon-containing coating (10) on the underside (6) of the substrate (2) contains at least 70%, particularly preferably at least 90%, sp2-configured carbon.
10. Device according to one of the preceding claims, characterized in that the diamond layer (8) is doped, wherein the doping preferably contains boron and/or phosphorus and/or nitrogen.
11. Device according to one of the preceding claims, characterized in that the diamond layer (8) 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.
12. Device according to one of the preceding claims, characterized in that the underside (6) of the substrate (2) also has a diamond coating on which and/or under which the carbon-containing coating is arranged.
13. Method for coating a top surface (4) of an aluminium nitride substrate (2) with a diamond layer (8) in a CVD reactor, the method comprising the following steps: a. Etching the top surface (4) outside the reactor with an etchant, so that a prepared top surface (4) is formed, b. Germinating the prepared top surface (4) with diamond particles, c. Positioning the substrate with the germinated upper side (4) on a sample table, wherein the substrate is supported on at least one support, d. Positioning the sample table with the substrate (2) in the reactor, e. Heating the reactor and the substrate (2) to an operating temperature and f. Deposition of the diamond layer (8) on the top surface (4) and a carbon-containing coating (10) containing at least 50% sp2-configured carbon on a bottom surface (6) of the substrate (2).
14. Method according to claim 13, characterized in that in a further process step a diamond layer (8) is deposited on the underside (6) of the substrate (2), wherein the substrate (2) is preferably turned over beforehand.

Description

The invention relates to a device with an aluminum nitride (AlN) substrate having a top surface and a bottom surface opposite the top surface, the surface being coated with a diamond layer. The invention further relates to a method for coating the surface of an aluminum nitride substrate with a diamond layer in a CVD reactor. It is known from the prior art to apply a diamond layer to a substrate in order to utilize the often advantageous properties of diamond. For example, electrodes for electrochemical cells are coated with a doped diamond layer to exploit the fact that the diamond layer is chemically inert and mechanically and thermally very stable, with the doping being necessary to increase the conductivity of the otherwise electrically insulating diamond layer. In other applications, the mechanical hardness and durability of diamond are utilized. To deposit a diamond layer onto a substrate, such as a silicon single crystal, a CVD reactor is often used. CVD stands for "chemical vapor deposition." The CVD process has been known for a long time as state of the art. The carbon necessary for the formation of the diamond layer is obtained from methane introduced into the reactor. The challenge lies in selecting the process parameters so that a diamond layer, and not some other possible carbon layer, is deposited. If a single crystal, such as silicon, is used as the substrate, the adhesion of the deposited diamond layer is generally strong enough to bond the coated surface. to use a substrate suitable for the respective application. A substrate coated on both sides with a diamond layer, intended as an electrode for electrochemical applications, is made from the DE 10 2021 110 587 A1 The type and quality of the deposited diamond layer depend on a number of parameters that must be set as precisely as possible. This applies, for example, to the temperature in the DE 696 29 980 T illuminated. Prior art attempts have been made to coat aluminum nitride substrates, i.e., ceramic substrates, with a diamond layer using the CVD process. This is, for example, the DE 197 10 202 A1 and the CN 1 13 755 819 A to extract. However, this resulted in poorer adhesion of the deposited diamond layer to the substrate than expected and required. An aluminum nitride substrate according to the present invention is an aluminum nitride ceramic which may additionally contain additives used in the production of the ceramic to influence its chemical, thermal, and/or mechanical properties, often subjecting it to a sintering process. Coating an aluminum nitride ceramic is therefore difficult for several reasons. One problem is the presence of metallic aluminum residues, meaning areas of varying sizes, which can melt at the high temperatures encountered during CVD coating. Aluminum has a melting point of approximately 660 °C. Temperatures in a CVD reactor can reach up to 900 °C, causing metallic aluminum to melt. The substrate becomes liquefied at the surface where metallic aluminum is present and can therefore no longer be coated with a diamond layer. Furthermore, due to the high vapor pressure of aluminum, a significant portion can transition into the gaseous state, severely contaminating both the coating deposited from the gaseous atmosphere within the CVD reactor and the reactor itself. This necessitates extensive, time-consuming, and costly cleaning before the reactor can be reused. Another problem can be the often unknown additives, such as Y₂O₃, that are added to the ceramic. Since their composition, melting points, boiling points, or gas pressures are often unknown, it is difficult to predict how the additives will behave when coating the substrate surface and whether they will even withstand or be suitable for coating. Another difficulty lies in the fact that the aluminum nitride substrate and the diamond layer to be deposited have very different crystallographic properties. The aluminum nitride is a polycrystalline ceramic, with the aluminum nitride crystal exhibiting an hdp lattice. The abbreviation hdp stands for "hexagonal close-packed." The diamond layer, on the other hand, grows in a cubic crystal lattice, with the (111) plane of this cubic lattice exhibiting a large mismatch to the hgp lattice. The invention is based on the objective of improving a device according to the preamble of claim 1 and of proposing a method by which a surface of an aluminium nitride substrate can be coated with a diamond layer in a CVD reactor. The invention solves the stated problem by a device with an aluminum nitride substrate having a top surface and a bottom surface opposite the top surface, wherein the top surface is coated with a diamond layer, wherein the device is characterized in that a coated area of the bottom surface has a carbon-containing coating containing at least 50% sp2-configured carbon, and a free area of the bottom surface has a thinner carbon-containing coating than the coated area, wherein, regardless of the thickness profile