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

The adsorption and decomposition of phosphine molecules on clean Si(100) 2 x 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 degrees C the phosphine mainly dissociatively adsorbs, most likely into P-P dimers. Near defect sites nondissociative adsorption of PH3 is also found. For temperatures up to about 400 degrees C surface diffusion allows the generation of small P-P dimer rows. Above 400 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 calculations suggest that these may result from surface stress induced by the phosphorus overlayer.