Reactions of Atomic and Molecular Fluorine on Silicon Surfaces

Abstract

AbstractThe reactions of atomic and molecular fluorine on silicon surfaces have been studied using x-ray photoelectron spectroscopy (XPS) and an ultrahigh vacuum (UHV) compatible microwave discharge effusive beam source of reactive species. The results indicate that molecular fluorine is dissociatively chemisorbed to form SiF2-like species on the surface. This reaction saturates at approximately monolayer surface coverage. Atomic fluorine also reacts initially to form SiF2-like surface species. Once the available surface sites are occupied, however, the fluorine atoms penetrate and react with silicon in the underlying layers. As the fluorine uptake increases, many of the subsurface silicon atoms become fully fluorinated. That is, the reaction product becomes SiF4-like. In contrast, preliminary studies indicate little difference in the behavior of atomic and molecular chlorine. These findings are compared with previous results for XeF2 adsorption, and their implications for plasma etching mechanism definition are discussed.