The decomposition of trumethylgallium, triethylgallium and trimethylaluminum on Si(100)

Abstract

This paper summarizes the results of a series of previous papers where the decomposition of trimethylgallium (TMGa), triethylgallium (TEGa), and trimethylaluminum (TMAI) on Si(100) wasstudied using TPD, XPS, EELS, and molecular beam techniques. The results show that a low coverges, the TMGa adsorbs molecularly. It then undergoes a series of intramolecular hydrogen transfer processes to yield methane, hydrogen, gallium, and adsorbed carbon. At higher exposures it is also possible to transiently populate a weakly bound state on top of the first monolayer of TMGa. The weakly bound TMGa decomposes above 450 K to yield dimethylgallium (DMGa) and CH x ( X = 3,4) groups. The DMGa and some of the CH x groups also desorb. However, some CH x groups remain bound to the substrate. There also is evidence for formation of traces of monomethylgallium. TMAI adsorbs as dimers. The dimers decompose upon heating to 400 K. Thereafter, the chemistry of TMAI decomposition is similar to that for TMGa except that methyl groups in the first monolayer of TMAI have a tendency to migrate to the silicon substrate. TEGa adsorbs as a monomer. It then decomposes via a β-hydrogen elimination process, producing ethylene. This pathway does not deposit carbon. At low temperatures and high incident TEGa fluxes there is a reaction pathway involving trapping of C 2H x groups which does deposit carbon. However, this is a minor reaction pathway. These results explain why TEGa is a much better source gas than TMGa when one needs to produce films with low carbon levels.