RF thermal plasma CVD of diamond: the role of acetylene in film morphology

Summary form only given. Diamond films produced by chemical vapor deposition (CVD) show faceting which is characterized by {100} or {111} surfaces. Many investigators have found that the morphology is systematically affected by substrate temperature, but contrary trends have been reported in the literature. In particular, some thermal plasma and combustion flame results have indicated that higher substrate temperatures shift the faceting from {111} to {100}, while most other results have indicated just the opposite. In this work we report that these contrary trends can be explained by the relative abundance of acetylene at the diamond surface during film growth. Diamond film growth experiments were conducted using an RF (3.2 MHz) plasma torch operating in the pressure range 267-1013 mbar (200-760 Torr). The plasma consists of argon and hydrogen with injected methane. Gas was sampled through a micro-orifice in the center of the film growth substrate and delivered to a gas chromatograph (GC), which provides measurements of several stable chemical species. A detailed two-dimensional numerical model was developed of the flow and chemistry in the region between the torch exit and the substrate, including the effect of the sampling orifice, and chemistry in the gas sampling line was modeled assuming plug flow.