GAS-PHASE STUDY WITH CF4 AND CCL2F2 ADDITION IN MICROWAVE CVD DIAMONDGROWTH

The effects of halogenated precursor associated with O-2 addition in t he gas phase for diamond growth have been studied. Optical emission sp ectroscopy (OES) and exhaust gas mass spectrometry (MS) were used in a microwave plasma-assisted chemical vapor deposition (MWPACVD) reactor . The relative emission intensity of atomic hydrogen line H-alpha (656 .3 nm) has been measured with CF4 and CCl2F2 concentrations in the ran ge of 0-5%. Our results show an increase of atomic hydrogen concentrat ion up to 80 and 200% when CF4 and CCl2F2 are added in the mixture, re spectively. The input gases were chosen in order to discern the oxygen effects for mixtures with different concentrations of CF4 and CCl2F2. An additional increase of 50% H generation was observed when O-2 was added in the range of 0-3% for both mixtures with 3% of CF4 or CCl2F2. Mass spectrometry was used to analyze the dissociation process of CF4 and CCl2F2 associated with HF and HCl formation, These dissociation p rocesses are correlated with the increase of atomic hydrogen concentra tion. For oxygen addition, CO formation is the main final product from the halocarbon. The higher thermodynamic stability of CO enables us t o obtain a gas phase with a high concentration of atomic hydrogen and inhibits the formation of solid non-diamond carbon observed in mixture s with high halocarbon concentrations. (C) 1998 Published by Elsevier Science S.A.