THE EFFECTS OF SURFACE-COMPOSITION IN THE REACTION OF TRIMETHYLGALLIUM ON SI(100) AND ON ALUMINUM AND GALLIUM TREATED SI(100)

The adsorption and decomposition of trimethylgallium (TMGa) on clean S i(100) and on gallium and aluminum covered Si(100) is examined with te mperature desorption spectroscopy (TDS) and Auger electron spectroscop y. At coverages below 2.5 x 10(13) TMGa molecules/cm2 on clean Si(100) , dosed at 100 K, the TDS products are methane (370 K, 500 K), hydroge n (800 K) and atomic gallium (970 K). At coverages near 0.5 x 10(14) m olecules/cm2 additional products, TMGa (370 K) and ethylene (570 K), a re observed. At multilayer coverages, 2.5 x 10(14) molecules/cm2, ther e are new desorption signals which result from the multilayer desorpti on peak of TMGa (140 K), and the desorption of dimethylgallium (350-55 0 K), monomethylgallium (550-750 K), a second ethylene peak (740 K), a nd methyl species (770 K). The presence of 0.3 ML or more of gallium o r aluminum on Si(100) drastically alters the reaction pathway, desorpt ion of TMGa is favored on the gallium treated surface, whereas decompo sition is favored on the clean silicon surface. More than twice as muc h gallium is deposited from TMGa on the untreated Si(100)2 x 1 surface than on a 0.5 ML gallium treated Si(100) surface. On the aluminum tre ated surface, desorption of gallium organometallic species is complete ly suppressed above the multilayer desorption temperature (140 K) and instead methyl groups are transferred from TMGa to aluminum atoms. Tri methylaluminum (TMAl) and dimethylaluminum (DMAl) are detected as deso rption products, desorption of these species increases with increased aluminum coverage. There is more net gallium deposited from TMGa on th e 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 su rface metal dimers on the gallium and aluminum treated Si(100) surface s, allows for facile transfer of methyl groups between the adsorbate a nd the surface metal atoms. The higher methyl-Al bond strength than th e methyl-Ga bond strength accounts for the irreversible formation of T MAl on the aluminum treated Si(100). On all of the surfaces, desorptio n of organometallics dominates over deposition of gallium as TMGa cove rage is increased above a monolayer.