Optical emission diagnostics of permanent and pulsed microwave discharges in H2–CH4–N2 for diamond deposition

Abstract

A microwave plasma of H2–CH4–N2 gas mixture used for diamond film deposition has been characterized by optical emission spectroscopy in the continuous and in the pulsed modes. In the continuous mode, a dynamic form of actinometric optical emission spectroscopy was used to determine temporal trends in the concentrations of H, CH and CN species following the cut-off of either the CH4 or N2 flows. These data show that the gas-phase reactions play a major role in the production of the above-mentioned species, but also the plasma–diamond surface reactions contribute significantly to the production of the CN radical. In the pulsed-discharge mode, time-resolved optical emission spectroscopy was used to determine the evolution of the relative concentrations of reactive species H, CH, CN and Ar with time. This evolution during the discharge, post-discharge and transient stages gives information on the processes leading to the population of excited states.