Photoeffects on the fluorination of silicon. II. Kinetics of the initial response to light

Abstract

When a silicon surface etched by XeF2 is illuminated with visible laser radiation, strong changes are observed in product formation rates. Initial rates of change of the products SiF, SiF2, SiF3, and SiF4 have been determined as a function of doping, pressure, and light intensity. Analysis of the kinetics has provided new insight into the mechanism by which radiation influences the etch rate. In particular, it has been found that initial rates of the species SiF4, SiF2, and SiF exhibit an approximately quadratic dependence on the laser intensity, while SiF3 appears to depend on its fourth power. It is proposed that trapping of electrons and holes by fluorine and silicon fluoride centers at or near the surface greatly increases their reaction rate. Modeling confirms this picture and provides some estimates for the relative magnitudes of rate constants for essential processes.