The Adsorption of Carbon Monoxide on Silicon and Gallium Arsenide Surfaces.

Mechanistic understanding of the reactions involved in etching, passivation, and growth techniques for fabricating microelectronic devices is aided by study of simpler model reactions at semiconductor surfaces. For example, desorption of CO by electron or photon stimulation from a semiconductor surface is a base model for the stimulated desorption of etch products from the same surface. This dissertation summarizes the results of a basic scientific study of the interactions between gaseous carbon monoxide (CO) and surfaces of silicon (Si) and gallium arsenide (GaAs). Specifically, it describes a study of CO adsorbed on the Si(100)-(2 x 1) and GaAs(100)-c(8 x 2) surfaces at both 110 R and room temperature. X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, low-energy electron diffraction, and temperature-programmed desorption techniques were used to monitor the reaction between the CO adsorbate and the semiconductor surfaces. The ultimate goal of the work in this dissertation was to show, using a variety of spectroscopic techniques, that CO does adsorb on semiconductor surfaces at both room temperature as well as at temperatures below 120 degrees Kelvin (K). The motivation for this work has been two -fold. First, the preparation of reproducible and well -characterized CO-dosed surfaces is required for future dynamical studies of the desorption event, the results of which can be used as a first model for the desorption of etch product molecules which leave semiconductor surfaces during processing. The second motivation has been to generate a model for CO adsorption at semiconductor surfaces which can be compared with the current understanding of the adsorption of CO on transition metal surfaces. It has been shown that CO adsorbs on a number of transition metal surfaces through its 5sigma molecular orbital. Prior to the work presented in this dissertation, no description of the bond formed between CO and room-temperature Si or GaAs had been published. Presented in this dissertation are photoelectron spectra that show CO does adsorb on the Si(100)-(2 x 1) and GaAs(100)-c(8 x 2) surfaces at both liquid nitrogen temperatures (110 K) and at room temperature (305 K). Also, the photoelectron spectroscopy studies presented here show that the type of interaction between the CO molecule and the semiconductor surface depends on the temperature of the surface during the adsorption experiment. Thermal desorption experiments from CO-dosed silicon prepared at room temperature indicate an activation energy for desorption which is significantly larger than that of the typical physisorption system. Finally, by using hot filaments to activate the CO prior to adsorption, evidence for an activation barrier to adsorption on Si has been found and is presented here.