FIELD OF INVENTION

Certain embodiments of the present invention relate to a method of conformally coating non-planar and/or non-refractory substrates with synthetic diamond material using a microwave plasma chemical vapour deposition (CVD) synthesis technique. Certain further embodiments of the present invention relate to non-planar and/or non-refractory polycrystalline CVD synthetic diamond components including non-planar and/or non-refractory components conformally coated with high quality polycrystalline CVD synthetic diamond material.

BACKGROUND OF INVENTION

Synthetic CVD diamond films can be grown using a variety of methods including hot filament, microwave plasma, and DC arc jet reactors. Each of these methods has its virtues. DC arc jet deposition systems tend to have high localized growth rates, but suffer from electrode/nozzle erosion, high gas consumption, and relatively poor area coverage. Hot filament reactors can coat large areas and three dimensional shapes but with limited film thickness and with relatively poor quality diamond material. In contrast, microwave plasma CVD synthetic diamond has become established as the leading method for producing high quality, bulk diamond material in the form of planar free-standing polycrystalline wafers. Unfortunately, microwave plasma methods have only limited capabilities to coat non-planar substrates due to adverse interactions between the microwave electric field and the non-planar substrates or work-pieces being coated. Coating of even simple three dimensional shapes such as tool inserts or loudspeaker dome mandrels is made difficult by the effects of electric field concentrations at external corners or conversely the weakness in electric fields at internal corners. This variation in the electric field adversely affects uniformity of both quality and thickness of the diamond film. For example, to date microwave plasma CVD reactors has not been successfully be used to conformally coat cutting tool inserts. At the corners of such cutting tool inserts high electric fields lead to thickening and rounding of the critical cutting edges, thus making them unsuitable for their intended purpose.

Non-refractory materials such as silicon that are thermally sensitive in terms of melting point or thermal shock are also challenging to coat uniformly in a microwave plasma reactor as the microwave plasma tends to damage the non-refractory substrate material.

In light of the above, what is needed is a method to conformally coat non-refractory substrates and/or three-dimensional (i.e. non-planar) shapes, such as cutting tool inserts and loudspeaker dome mandrels, using a microwave plasma CVD diamond synthesis technique which will result in high quality polycrystalline CVD diamond material uniformly coated over the surface of the substrate material without undue rounding and thickening at edges and corners and/or without unduly damaging the substrate material.

It is an aim of certain embodiments of the present invention to solve the aforementioned problems.

SUMMARY OF INVENTION

According to a first aspect of the present invention there is provided a method of coating a non-refractory and/or non-planar substrate with synthetic diamond material using a microwave plasma chemical vapour deposition (CVD) synthesis technique, the method comprising:forming a composite substrate assembly comprising:a support substrate comprising an upper surface; one or more electrically conductive refractory guards disposed over the upper surface of the support substrate and extending to a height hgabove the upper surface of the support substrate; andone or more non-refractory and/or non-planar substrates disposed over the upper surface of the support substrate and extending to a height hsabove the upper surface of the support substrate, wherein the height hsis less than the height hg, wherein a difference in height hg−hslies in a range 0.2 mm to 10 mm;placing the composite substrate assembly within a plasma chamber of a microwave plasma CVD reactor;feeding process gases into the plasma chamber including a carbon containing gas and a hydrogen containing gas;feeding microwaves in the plasma chamber to form a microwave plasma at a location over the composite substrate assembly; andgrowing synthetic diamond material on the one or more non-refractory and/or non-planar substrates.

According to a second aspect of the present invention there is provided a composite component comprising:a non-planar base;and a polycrystalline CVD synthetic diamond coating on a surface of the non-planar base,wherein the non-planar base has a longest linear dimension when projected onto a plane of no less than 5 mm,wherein the polycrystalline CVD synthetic diamond coating has a thickness in a range 5 to 100 μm,wherein the thickness of the polycrystalline CVD synthetic diamond coating varies by no more than 75% of an average thickness of the polycrystalline CVD synthetic diamond coating, excluding any tapering at the peripheral edge of the polycrystalline CVD synthetic diamond coating,wherein the polycrystalline CVD synthetic diamond coating comprises micron scale inter-grown diamond grains and a low sp2 carbon content indicative of a microwave plasma CVD synthesis technique, andwherein the polycrystalline CVD synthetic diamond coating has no cracks which extend greater than 2 mm in length.

