PHOTOEMISSION-STUDY OF LOW-PRESSURE HYDROGEN AND DISILANE ADSORPTION ON SI(111) 7 X 7 AND GE(111)

We report results on the adsorption of hydrogen and disilane on Si(111) 7 × 7 and Ge(111) surfaces studied by ultraviolet and X-ray (XPS) photoemission spectroscopies. Samples were heated in the 20-500°C temperature range and exposed to low pressure (10-5 torr) H and Si2H6 doses in the 103-105 L exposure range. Only characteristic signatures of mono- and dihydride phases are observed. Saturation of a silicon surface with Si2H6 cannot be achieved at room temperature (RT) in contrast with experiments carried out in the same conditions with atomic hydrogen. Results suggest formation of a more or less amorphous polysilane. A Si(111) surface saturated at 300°C with monohydride phase cannot subsequently adsorb Si2H6 at room temperature whereas further hydrogen adsorption is still possible through dihydride phase formation. Dihydride phase formation is possible by disilane cracking at a hot tungsten filament. Disilane adsorption on a Ge(111) surface induces characteristic features of mono- and dihydride phases. No silicon deposit is evidenced by XPS at room temperature. Silicon deposition on the Ge(111) surface requires disilane cracking at a hot tungsten filament. Possible mechanisms explaining the observed results are discussed. © 1990.