The chemistry of gallium deposition on Si(001) from trimethylgallium: An atomically resolved STM study

The chemistry of trimethylgallium (TMG, Ga(CH3)(3)) and its dissociation fragments on the Si(001) surface has been studied using scanning tunneling microscopy (STM). The products of TMG dissociation are identified by their bonding location with respect to the underlying Si(001) lattice, by bias-dependent imaging and from detailed counting statistics. TMG dissociates at room temperature, yielding a methyl group and a dimethylgallium fragment which bind to the surface. The Ga(CH3)(2) groups produced by TMG dissociation are somewhat mobile at room temperature but are bonded more strongly near surface defects. Further dissociation yields gallium atoms on the surface, but no additional methyl groups. It is proposed that this second stage of reaction involves an intramolecular reaction to produce ethane, which desorbs into the gas phase, and gallium atoms. The gallium atoms are observed to arrange into single rows of gallium dimers which bind epitaxially on the Si surface. Heating the surface to 150 degrees C completely decomposes the DMG fragments, yielding Ga atoms and CH3 groups.