Temperature and concentration distribution of H2 and H atoms in hot-filament chemical-vapor deposition of diamond

Abstract

The temperature and concentration distributions of hydrogen in a hot-filament chemical-vapor deposition reactor of diamond have been measured simultaneously by coherent anti-Stokes Raman scattering (CARS). The bright background from the filament was rejected by using CARS and gating on the detector as well as spatial filtering. The CARS spectra provided direct and accurate measurements of the H2 temperature and concentration distributions. The concentration distribution of atomic hydrogen was also determined by assuming a constant pressure condition and equilibrium between translational and rotational degrees of freedom in the system. These temperature and concentration distributions are essential for the understanding and modeling of the diamond growth processes. It was found that the H-atom distribution departed substantially from the thermal equilibrium prediction except very near the filament; however, a diffusion-controlled model predicted the slope of this distribution throughout the measured region.