Thermal resistance and electrical insulation of thin low-temperature-deposited diamond films

Abstract Diamond layers only a few microns thick were deposited by microwave plasma-assisted chemical vapour deposition (CVD) on silicon at different substrate temperatures (500, 550 and 800°C) using different methods for nucleation enhancement (ex situ mechanical pretreatment or in situ substrate biasing). The thermal resistance was measured for conduction normal to these thin layers, which span a wide range of structural properties from random small-grained over columnar to highly oriented grain structures. It was shown that the thermal resistance normal to thin CVD diamond layers depends strongly, for a given layer thickness, on the grain size and the degree of grain orientation in the direction of growth. The smallest thermal resistances were observed for bias-nucleated, highly oriented films deposited at 800°C with pronounced fibre textures. An upper limit for the effective thermal resistance of the diamond-silicon boundary of 1.8 × 10 −9 m 2 K/W was determined for mechanically pretreated, columnar-grained films deposited at low temperatures, which suggests a small interfacial disorder for these films. Furthermore, the electrical insulation of the low-temperature deposited films was shown to be comparable with that of high-temperature-deposited diamond.