PHOSPHINE ADSORPTION AND DECOMPOSITION ON SI(100) 2X1 STUDIED BY STM

The adsorption and decomposition of phosphine molecules on clean Si(10 0) 2 x 1 surfaces have been investigated by scanning tunneling microsc opy, photoemission spectroscopy, and total energy calculations. Phosph ine decomposition depends strongly on the substrate temperature and re sults in a variety of surface structures depending on the relative rat es of phosphine adsorption, hydrogen and phosphorus desorption, and hy drogen, phosphorus, and silicon surface diffusion. Between room temper ature and 200 degrees C the phosphine mainly dissociatively adsorbs, m ost likely into P-P dimers. Near defect sites nondissociative adsorpti on of PH3 is also found. For temperatures up to about 400 degrees C su rface diffusion allows the generation of small P-P dimer rows. Above 4 00 degrees C, beyond the onset of hydrogen desorption, larger islands with width not exceeding approximately eight dimer rows are formed. At maximum phosphorus coverage, obtained by phosphine adsorption at 625 degrees C, straight vacancy lines are found, which most likely consist of phosphorus passivated Si(111) microfacets. Total energy calculatio ns suggest that these may result from surface stress induced by the ph osphorus overlayer.