Modelling radiative properties of participating species in a microwave plasma reactor for diamond deposition

Abstract

The paper details the modelling of radiation in a microwave assisted plasma reactor used to deposit synthetic diamond over a substrate. The main radiatively active constituents in the reactor are atomic and molecular hydrogen, acetylene, methane and soot (if produced). Radiation from hydrogen occurs in ultraviolet (UV) whereas the hydrocarbons are active in the infrared region. Soot absorb and scatter in the UV but only absorption is important in the infrared-visible (IR-V) region. Hence, the two spectral regions have been treated independently. A two temperature model has been adopted for hydrogen thermodynamic state where Tg represents rotational, vibrational and translational temperature and Te represents electronic excitation temperature. As scattering is significant in UV, the radiative transfer equation is solved using Discrete Ordinate Method (DOM) with cumulative-k narrow-band model for molecular hydrogen. Radiation from atomic hydrogen has been found to be negligibly small compared to molecular hydrogen. In the IR-V, radiative transfer equation is solved using ray tracing method with gas properties represented by statistical narrow-band models. Preliminary simulations for reactor conditions indicate that soot significantly increase the radiative transfer in the reactor and presence of soot can disrupt the operation of the plasma reactor.