Phosphine adsorption and decomposition on Si(100) 2 x 1 studied by STM.

Abstract

The adsorption and decomposition of phosphine molecules on clean Si(100) 2\ifmmode\times\else\texttimes\fi{}1 surfaces have been investigated by scanning tunneling microscopy, photoemission spectroscopy, and total energy calculations. Phosphine decomposition depends strongly on the substrate temperature and results in a variety of surface structures depending on the relative rates of phosphine adsorption, hydrogen and phosphorus desorption, and hydrogen, phosphorus, and silicon surface diffusion. Between room temperature and 200 \ifmmode^\circ\else\textdegree\fi{}C the phosphine mainly dissociatively adsorbs, most likely into P-P dimers. Near defect sites nondissociative adsorption of ${\mathrm{PH}}_{3}$ is also found. For temperatures up to about 400 \ifmmode^\circ\else\textdegree\fi{}C surface diffusion allows the generation of small P-P dimer rows. Above 400 \ifmmode^\circ\else\textdegree\fi{}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 \ifmmode^\circ\else\textdegree\fi{}C, straight vacancy lines are found, which most likely consist of phosphorus passivated Si(111) microfacets. Total energy calculations suggest that these may result from surface stress induced by the phosphorus overlayer.