SURFACE-REACTION MECHANISMS ON SI(111)-(7X7) DURING SILANE UHV-CVD

We report an STM study of the Si(111)-(7 x 7) surface after silane ads orption in the temperature range 700-800 K. At these temperatures, we show that the decomposition of the adsorbed species and their subseque nt diffusion lead to the etching of Si adatoms from the dimer adatom s tructure (DAS) and to the formation of hydrogenated silicon-atom clust ers on the faulted part of the unit cell. We have also studied the ste ady state of the surface under static silane pressure. We conclude tha t hydrogen desorption occurs from these clusters, leading to a first-o rder desorption process. (C) 1997 Elsevier Science B.V.