Growth of homoepitaxial single crystal diamond by microwave plasma CVD in H₂-CH₄-O₂ gas mixtures at high microwave power densities

Single crystal diamond growth by microwave plasma assisted CVD in oxygen-containing gas mixtures is attractive in view of possibility to realize a prolonged non-stoped synthesis process and to minimize defects and impurities in the produced material. We studied the homoepitaxial diamond growth on (100) oriented substrates in H₂-CH₄-O₂ environment at high pressures (300 Torr) and high microwave power density (≈400 W/cm³) at variable O₂ content (up to 3.5 %) in the plasma. A low-coherence optical interferometry and optical emission (OE) spectroscopy was used to measure in situ the growth rate and probe the plasma chemistry, respectively. Depending on CH₄ content the growth rate dependence on the concentration [O₂] either shows a maximum at certain [O₂], or a monotonic decline, up to complete stop of the growth at some critical O₂ percentage (specific for each methane content) in the mixture. We found CH, H_β, C₂ and C₃ lines in OE spectra from the plasma to monotonically quenched with O₂ adding, particularly, disappearance of the C₂ line coincidences with growth rate going to zero. High-quality homoepitaxial diamond layers were produced at moderate growth rate at optimal gas composition and characterized with Raman spectroscopy. Moreover, a significant reduction in the stress on (111) oriented substrates owing to O₂ addition was observed.