The effects of surface composition on the reaction of trimethylgallium on Si(100) and on aluminum and gallium treated Si(100)

Abstract

The adsorption and decomposition of trimethylgallium (TMGa) on clean Si(100) and on gallium and aluminum covered Si(100) is examined with temperature desorption spectroscopy (TDS) and Auger electron spectroscopy. At coverages below 2.5 × 10 13 TMGa molecules cm 2 on clean Si(100), dosed at 100 K, the TDS products are methane (370 K, 500 K), hydrogen (800 K) and atomic gallium (970 K). At coverages near 0.5 × 10 14 molecules cm 2 additional products, TMGa (370 K) and ethylene (570 K), are observed. At multilayer coverages, 2.5 × 10 14 molecules cm 2 , there are new desorption signals which result from the multilayer desorption peak of TMGa (140 K), and the desorption of dimethylgallium (350–550 K), monomethylgallium (550–750 K), a second ethylene peak (740 K), and methyl species (770 K). The presence of 0.3 ML or more of gallium or aluminum on Si(100) drastically alters the reaction pathway, desorption of TMGa is favored on the gallium treated surface, whereas decomposition is favored on the clean silicon surface. More than twice as much gallium is deposited from TMGa on the untreated Si(100)2 × 1 surface than on a 0.5 ML gallium treated Si(100) surface. On the aluminum treated surface, desorption of gallium organometallic species is completely suppressed above the multilayer desorption temperature (140 K) and instead methyl groups are transferred from TMGa to aluminum atoms. Trimethylaluminum (TMA1) and dimethylaluminum (DMA1) are detected as desorption products, desorption of these species increases with increased aluminum coverage. There is more net gallium deposited from TMGa on the aluminum treated Si(100) surface than on the gallium treated surface or on the untreated Si(100) surface. It is postulated that a 3-center, 2-electron bonding arrangement, between the adsorbed TMGa and the surface metal dimers on the gallium and aluminum treated Si(lOO) surfaces, allows for facile transfer of methyl groups between the adsorbate and the surface metal atoms. The higher methyl-Al bond strength than the methyl-Ga bond strength accounts for the irreversible formation of TMAl on the aluminum treated Si(100). On all of the surfaces, desorption of organometallics dominates over deposition of gallium as TMGa coverage is increased above a monolayer.