Simulations of the hot-filament diamond CVD gas-phase environment: direct comparison with experimental measurements

The CHEMKIN suite of computer programs (Sandia Labs) has been used to simul ate the mole fractions of the important gas phase species within a hot fila ment CVD diamond reactor. These simulations have been compared to data meas ured using an in-situ molecular beam mass spectrometer. Excellent agreement between simulation and experiment was obtained by using just two fitting p arameters. The first of these, the local gas temperature, was found to be a relatively insensitive parameter, and values could be varied by several hu ndred degrees centigrade with no appreciable effect on the results of the c alculation. However, the second parameter, the mole fraction of hydrogen at oms, was found to be very important since it controlled the whole gas-phase chemistry. Comparison of experimental data with simulations, therefore, ha s allowed us to derive absolute mole fractions of not only the stable hydro carbon species, but also the methyl radicals and the hydrogen atoms, simult aneously, during a typical CVD process. These results are presented as a fu nction of filament temperature. (C) 1999 Elsevier Science S.A. All rights r eserved.