Decomposition of trimethylgallium on Si(100): Spectroscopic identification of the intermediates

Abstract

The decomposition of trimethylgallium (TMG) on a heated Si(100) substrate is studied using TPD, XPS and EELS. It is found that the decomposition of TMG is largely an intramolecular process. The TMG adsorbs molecularly at low temperatures. Upon heating, one of the methyl groups in the TMG reacts with a hydrogen on another methyl group liberating methane. This leaves a CH 2 group bound to the gallium which is seen clearly with EELS. Upon further heating, another hydrogen reacts with the remaining methyl group producing additional methane. Simultaneously, the remaining fragments decompose into gallium atoms and CH groups. The CH groups dissociate above 750 K yielding adsorbed hydrogen and adsorbed carbon. The hydrogen desorbs between 750 and 850 K while the carbon gets incorporated into the growing film. These results show that carbon incorporation is an intrinsic part of the TMG decomposition process. Thus, TMG would not be an appropriate source gas when one needs to produce films with very low carbon levels.