Evaluation of a substrate pretreatment for hot filament CVD of diamond

Abstract

The absolute concentration of methyl radicals (CH₃) and the mole fraction of acetylene (C₂H₂) are measured in a hot filament chemical vapor deposition (CVD) system both during and after an initial pretreatment that has been used successfully in microwave plasma and oxyacetylene torch CVD systems to produce more uniform and higher density crystal nucleation. The pretreatment technique, which consists of deposition for a relatively short time with a high input concentration of hydrocarbon in the feed gas, was studied for both methane (CH₄) and C₂H₂ as the input hydrocarbon diluted in H₂. Scanning electron micrographs of diamond films deposited under the conditions studied indicate that the pretreatment using CH₄ is not effective in increasing the crystal nucleation density, but is moderately effective in increasing the crystal size. The C₂H₂ pretreatment has no apparent effect upon either the crystal size or nucleation density. The spectroscopie measurements suggest that the surface condition of the filament is the prominent factor affecting the gas phase chemistry both during and after the pretreatment stage.