Thermal reactions of phosphine with Si(100): a combined photoemission and scanning-tunneling-microscopy study

This study investigates the adsorption and thermal decomposition of phosphi ne (PH3) on the Si(100)-(2 x 1) surface. The adsorption species, dissociati on reactions, atomic ordering, and surface morphology of the phosphine/Si(1 00) surface at temperatures between 300 and 1060 K are examined by scanning tunneling microscopy (STM) and high-resolution core-level photoemission sp ectroscopy employing synchrotron radiation. The P 2p core level spectra cle arly indicate that phosphine molecularly adsorbs at room temperature and pa rtially dissociates into PH2 and H on a time scale of minutes at low (<0.2M L) coverages. An exposure of >15 Langmuirs (L, 1 Langmuir=10(-6) Torr s(-1) ) of phosphine on the Si(100)-(2 x 1) surface at room temperature produces a saturated and disordered surface. The total amount of P on the saturated surface is ca 0.37 ML as calibrated by the P 2p photoemission intensity. Su ccessive annealing of the saturated surface at higher temperatures converts PH, into PH,, converts PH, to P-P dimers, and causes the desorption of PH3 . These processes become complete at similar to 700 K, and the resulting su rface is a H/Si(LOD)-(2 x 1) surface interspersed with one-dimensional P-P islands. Desorption of hydrogen from that surface occurs at similar to 800 K, and is accompanied by partial displacement of P with Si atoms on the sub strate. At 850 K, the Si(100) surface, interspersed with 0.22 ML of two-dim ensional islands, is a random alloy of nominal 0.5 ML Si-P heterodimers and 0.5 ML Si-Si dimers. (C) 1999 Published by Elsevier Science B.V. All right s reserved.