Semiempirical calculations of fluorine chemisorption on the Si(111)7*7 surface

Abstract

The chemisorption and etching of fluorine on the Si(111)7*7 surface has been studied using Si90H74Fn (1<or=n<or=5) clusters and the atom superposition and electron delocalization molecular orbital (ASEDMO) method. At low coverage, the fluorine atoms are adsorbed onto the dangling bonds. As more fluorines are added, however, a fluorine-bonded adatom is found to move from its original threefold site (one fluorine atom), to an adjacent bridge site (two fluorine atoms) and then to a neighbouring on-top site (three or more fluorine atoms), while the rest atoms remain fixed near their original threefold equilibrium sites. The lowest etching energy is found to be 0.35 eV for SiF4 desorption from a rest atom site.