THERMAL-RESISTANCE AND ELECTRICAL INSULATION OF THIN LOW-TEMPERATURE-DEPOSITED DIAMOND FILMS

Diamond layers only a few microns thick were deposited by microwave pl asma-assisted chemical vapour deposition (CVD) on silicon at different substrate temperatures (500, 550 and 800 degrees C) using different m ethods for nucleation enhancement (ex situ mechanical pretreatment or in situ substrate biasing). The thermal resistance was measured for co nduction normal to these thin layers, which span a wide range of struc tural properties from random small-grained over columnar to highly ori ented grain structures. It was shown that the thermal resistance norma l to thin CVD diamond layers depends strongly, for a given layer thick ness, on the grain size and the degree of grain orientation in the dir ection of growth. The smallest thermal resistances were observed for b ias-nucleated, highly oriented films deposited al 800 degrees C with p ronounced fibre textures. An upper limit for the effective thermal res istance of the diamond-silicon boundary of 1.8 x 10(-9) m(2)K/W was de termined 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-tempera ture deposited films was shown to be comparable with that of high-temp erature-deposited diamond. (C) 1997 Elsevier Science S.A.