Effect of Oxygen Component in Magneto-Active Microwave CH4/He Plasma on Large-Area Diamond Nucleation over Si

Nucleation-enhanced pretreatments have been studied for large-area diamond growth on Si (100) substrates using magneto-active microwave plasma chemical vapor deposition (CVD) at low pressures below 10 Pa. In this study, an optimal CO2 composition in the CH4/He plasma used for the pretreatment was mainly examined for the case of a low substrate temperature of ∼600°C. A two-hour subsequent growth using a CH4[5 sccm]/CO2[10 sccm]/H2[85 sccm] gas mixture after the pretreatment resulted in <100>-oriented growth of diamond Particles with a high density (∼109/cm2) on Si substrates pretreated at CO2 concentrations of 1–2%. On the other hand, at CO2 concentrations higher than these, the carbon films deposited during the pretreatment were less dense and were almost completely etched off after a 10-min treatment using the growth plasma. It was found that quadrupole mass spectra, optical emission spectra and Raman scattering spectra changed substantially when CO2 beyond 3.8% was added to the source gas.