OBSERVATION OF THE METHYL RADICAL DURING THE SURFACE DECOMPOSITION REACTION OF TRIMETHYLGALLIUM

We have studied the mechanism and kinetics of the decomposition reactions of trimethylgallium (TMG) in the presence of arsine. These studies were performed in a very low pressure pyrolysis (VLPP) reactor in the pressure range of 10(-2)-10(-3) Torr. We have observed the methyl radical product of the surface-catalyzed decomposition reactions of TMG using modulated beam mass spectrometry. The primary step in the decomposition of TMG involves the adsorption and the successive release of the methyl radicals from the surface. The apparent activation energy for the release of the methyl radical in the range of 400-575-degrees-C is 22 +/- 3 kcal/mol. This apparent activation energy is much lower than the average Ga-C bond energy in the gas phase of 60 kcal/mol and can probably be accounted for by the heat of adsorption and the concerted reactions on the surface. We have suggested an overall reaction scheme to explain our observations. The introduction of arsine increases the decomposition of TMG and the methyl radical production. However, the activation energy for the production of the methyl radicals is not affected by the presence of arsine. There is no evidence for the recombination of methyl and H species on the surface. At temperatures above 600-degrees-C there is a surprising decrease in the methyl radical signal. This has been attributed to the desorption of Ga(CH3)x species rather than methyl radicals.