Electron density in moderate pressure diamond deposition discharges

Abstract

The electron density is measured in a microwave plasma-assisted chemical vapor deposition diamond reactor at moderate pressures (5–60 Torr) using a millimeter-wave open resonator technique. The discharge plasma is generated using a resonant cavity excited at the frequency 2.45 GHz. The absorbed input power of 400 W generates a microwave discharge above a substrate holder located in a quartz dome. The discharge, shaped as a plasma ball or hemisphere, is positioned in the resonant path of the millimeter-wave open resonator operating at the frequency 32.2 GHz. The millimeter-wave open resonator operates with a quality factor of approximately 3500. The shift in the resonant frequency of the resonator when the discharge plasma is present allows the determination of the electron density. The electron densities measured were in the range of (1–6)×10 11 cm −3 for the pressure range of 5–60 Torr. Electron density measurements for various reactor parameter settings are presented for both pure hydrogen and hydrogen–methane mixture discharges.