Improved flow conditions in diamond hot filament CVD—Promising deposition results and gas phase characterization by laser absorption spectroscopy

Abstract

A hot filament plant for chemical vapor deposition of crystalline diamond featuring new operating stages has been built. It allows (i) a separate methane feed locally at substrate position and (ii) supplying a forced gas flow towards the substrate. To understand the effect of these two features on diamond growth, the results of systematic diamond growth experiments are discussed. To reveal the effects of these features on the gas phase, infrared tunable diode laser absorption spectroscopy (IR-TDLAS) was employed. Using a forced gas flow showed a remarkable increase in the diamond growth rate of a factor >6 compared to standard coating setups. By lowering the methane content in the forced flow diamond quality factors >95% were achieved. IR-TDLAS showed an increase of all measured carbon-containing species CH 4, C 2H 2, CH 3 and CO when applying the forced flow. The mass transport dominated by diffusion in the standard setup shifts to a convective gas transport in the forced flow setup. The induced laminar flow causes a more effective transport of the growth species to the substrate and leads to higher growth rates. Application of feeding methane locally at substrate position leads to exceptionally high growth rates (0.68 μm/h) at correspondingly high diamond quality (91%). For this, the methane content has to be lowered, though, which at the same time leads to a more homogenous deposition lateral on the surface. From the IR-TDLAS gas phase measurements, a more effective precursor dissociation, a higher CH 3 density and a rise in the CH 3⧸C 2H 2 ratio above the substrate surface can be derived.