DISSOCIATIVE ADSORPTION AND SITE-SPECIFICITY IN THE INITIAL-STAGES OFTETRAETHOXYSILANE (TEOS) INTERACTION WITH SI(111)-(7 X 7)

We report results of a scanning tunneling microscopy and X-ray photoel ectron spectroscopy study on the interaction of tetraethoxysilane (TEO S), a precursor for chemical vapor deposition of silicon dioxide, with Si(111)-(7 x 7) at room temperature. Under these conditions the inter action of TEOS with the surface is predominantly dissociative. The mai n adsorption products are ethyl- and triethoxysiloxane groups, which p robably evolve in a four-center reaction of TEOS with two neighboring surface dangling bonds. Adsorption of the dissociation products is hig hly site-selective: triethoxysiloxane groups adsorb on the Si adatoms while ethyl groups react with the rest-atom dangling bonds. Center ada toms are over three times more reactive towards this reaction than cor ner adatoms. This two-fold selectivity is explained within the concept of local electron donor/acceptor properties. (C) 1998 Elsevier Scienc e B.V.