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 magnetoactive 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 similar to 600 degrees C. A two-hour subsequent growth using a CH4 [5 sccm]/CO2[10 sccm]/H-2 [85 sccm] gas mixture after the pre treatment resulted in [100]-oriented growth of diamond Particles with a high density (similar to 10(9)/cm(2)) 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.