Numerical modeling of diamond growth environment in hfcvd reactors

Abstract

A numerical model of the diamond growth environment in a hot-filament chemical vapor deposition (HFCVD) system has been developed. The model combines equations of the conservation of mass, momentum, energy and chemical species with appropriate boundary conditions. The combined partial differential equations were solved numerically using the finite-volume method. Then the model was used to investigate the effects of gas-phase diffusion, CH, concentration and the filament temperature on the production of CH3 that is known as the diamond precursor in the HFCVD system. From the result, the predicted chemical species concentrations agreed well with previously measured experimental values and the concentration of CH~ is shown to increase as the CH4 concentration and the filament temperature increase. It is also known that, although acetylene (C_-H_0 is a dominant chemical species in the equilibrium state of the C-H system at filament temperature, methyl (CH~), which is a precursor of the diamond, is more plentiful than C~_H_, in a real HFCVD reactor because of the gas-phase diffusion.

Chemical Vapor Deposition of Diamond: An in Situ Study by Vibrational Spectroscopy

“…Beyond the advancements already achieved in the growth of diamond thin films by chemical vapor deposition (CVD) , there still are a number of important open issues including the further decrease of the temperature of the CVD process , without a loss in film quality. Another point into which considerable effort has been put is a comprehensive modeling. − Despite general agreement on a number of key steps and the success of models to reproduce many aspects of the CVD process, , discrepancies between simulation and experiment still exist, which indicate that essential aspects of the chemistry are not described properly by the models. This is highlighted by the comparison of a comprehensive simulation with experimental results from gas-phase spectroscopy which revealed diverging results of the gas-phase species near the substrate …”

“…Only at very low filament and substrate temperatures (Figure a) do structures which can be associated with CH 3 appear. Recalling that CH 3 is considered an essential species in diamond growth, , this could mean either that other species such as acetylene, which would appear at much higher wavenumbers, are responsible or that the CH 3 reacts so quickly that the concentration is below detection threshold. Preliminary experiments at higher wavenumber did not yield a significant signal, and therefore, we favor the second interpretation at present.…”