HYDROGEN DISSOCIATION IN A MICROWAVE-DISCHARGE FOR DIAMOND DEPOSITION

A mathematical model was developed to predict the degree of gas dissociation in an H2 microwave discharge sustained in a tubular reactor. Reaction rate coefficients for electron-particle reactions were determined by solving the Boltzmann equation for the electron energy distribution function (EEDF). These coefficients were parameterized and used in a plasma model to calculate the self-sustaining electric field, atomic hydrogen density and electron density in the plasma. The effects of total gas density (pressure), power, flow rate, and wall recombination probability were investigated. In the parameter range studied, gas dissociation was enhanced by lowering the total gas density and/or increasing power. Wall recombination did not affect the atom density for values of the recombination probability lower than 2 x 10(-4). Addition of 1 % CH4 to the hydrogen discharge had only a minor effect on the EEDF. Therefore, results reported here can also be used to calculate the electron-particle reaction rate coefficients in the H2/CH4 discharge. The model provides guidelines for controlling H2 dissociation in plasma chemical vapor deposition reactors used for diamond growth.