Examination of the chemistry involved in microwave plasma assisted chemical vapor deposition of diamond

Abstract

Chemical reaction products formed in a microwave plasma assisted chemical vapor deposition apparatus for diamond film deposition are detected using mass spectrometry. Carbon source gases CH₄, C₂H₆, C₂H₄, or C₂H₂ produce CH₄, C₂H₂, CO, and H₂O as major stable reaction products when introduced into a H₂/O₂ plasma under diamond deposition conditions. The effect of oxygen addition is similar for all carbon source gases with respect to reaction product formation, indicating that a common reaction mechanism is active in all cases. On a qualitative basis, these observations are consistent with a mechanism describing the oxidation of CH₄ in flames. No beneficial effects were observed using alternating growth/etch cycles to deposit films. Films grown using CH₄ as the carbon source gas consistently produce higher quality diamond films compared to films grown from C₂H₂.