LARGE AREA DIAMOND DEPOSITION IN HFCVD TECHNIQUE EMPLOYING CONVECTIVE FLOW OF GASES

Hot filament chemical vapour deposition technique is widely used for the synthesis of diamond at sub-atmospheric pressure. The normal procedure involves diffusional flow of the diamond precursor species and the atomic hydrogen, produced by the input gases at the heated filament. The active species are short lived and can therefore travel relatively small distances, in their lifetime, in an intrinsically slow diffusion controlled process. This restricts the distance between the filament and the substrate to less than or similar to 1 cm. In this communication, it is brought out that this shortcoming can be overcome, to a large extent, by using convective flow of gases. With minor modifications in the standard experimental set up, consisting of a single filament-jet assembly, it has been possible to deposit good quality diamond on zirconium substrate, placed at a distance approximately 5 cms from the filament and over an area approximately 7 cm2. Besides deposition on larger area, this concept minimises the problems associated with the close proximity of an intense localized heat source to the substrate.