Optical Emission Spectroscopy Of Microwave Plasma Chemical Vapor Deposition

The research of plasma parameters during microwave plasma chemical vapordeposition （MPCVD） of diamond is very important for preparation of high qualitydiamond film. The exiting radical and radical intensity was researched in differentmethane concentration、pressure and nitrogen concentration by optical emissionspectroscopy.（1） The plasma of CH₄/H₂was diagnosed with optical emission. The exitingradicals in the plasma and the influence of the methane concentration （0.5%-7%） andthe pressure （10-38kPa） on radical concentration and distribution were researched.The results indicate that the radicals of CH、H_α, H_β, H_γ, C₂and little impurity atomMo exit in the plasma. The intensity of emission spectrum of the radical increaseswith the increasing of the methane concentration, especially the intensity of C₂has anotable increase. The ratio of the intensity of the CH to Hαis unchanging with theincreasing of methane concentration, while that of C₂to Hαhas a marked increase.The uniformity of the space distribution of the radicals becomes worse with theincreasing of methane concentration, and the methane concentration should becontrolled within1%. The intensity of emission spectrum of CH、C₂and H_αwasincreased and than decreased with the increasing of the pressure, and the intensity ofthree spectroscopy lines reached its maximum when the pressure was30kPa. Theintensity ratio ofI_C2/I_Hαwas no change, the intensity ratio ofI_CH/I_C2decreasedrapidly with the increasing of the pressure and the intensity ratio was no change whenthe pressure was26kPa. The uniformity of the space distribution of the radicalsbecomes worse with the increasing of the pressure.（2） The plasma of CH₄/H₂/N₂was diagnosed with optical emission. The exitingradicals in the plasma and the influence of the nitrogen concentration （0-1%） and themethane concentration （0.25%-7%） on radical concentration were researched. Thediamond films of adding nitrogen and without nitrogen were investigated by Raman spectroscopy. The results indicate that the radicals of CH、H_α, H_β, H_γ, C₂andCN（388.04nm） exit in CH₄/H₂/N₂plasma. The intensity of Hαwas no change and theintensity of CH slightly decreased and the intensity of CN linearly increased and theintensity of C₂significantly reduced with the increasing of the nitrogen concentration.The intensity ratio ofI_CH/I_CNandI_C2/I_CNsignificantly decreased when thenitrogen concentration changed from0to0.1%and their intensity ratio slightlydecreased with the further increasing of the nitrogen concentration. The intensity ratioofI_C2/I_HαandI_CH/I_C2were no change with the increasing of the nitrogenconcentration, and the methane concentration should be controlled within2%. Theresults of Raman spectroscopy indicated that adding nitrogen can significantlyimprove the diamond phase content; it was conducive to prepare the high qualitydiamond film.