The controlled atomic layer growth of SiO2 insulating layers on silicon surfaces might be achieved through the sequential reaction of SiCl4 and H2O:
(A) Si-Cl + H2O → Si-OH + HCl
(B) Si-OH + SiCl4 → Si-O-SiCl3 + HCl.
To explore this ABAB… binary reaction scheme, laser-induced thermal desorption, temperature-programmed desorption, and Auger electron spectroscopy techniques were utilized to measure the kinetics of H2O oxidation of a Si(111)7×7 surface that had been previously subjected to a saturation SiCl4 exposure. Reaction kinetics studies for the oxidation of the chlorinated surface revealed that the rate of oxygen gain and the rate of chlorine loss were equal at reaction temperatures between 200 K and 700 K. These results were consistent with a direct substitution reaction according to:
(A) Si-Cl + H2O → Si-OH + HCl.
Above 700 K, the amount of oxygen gain became progressively greater than the amount of chlorine loss. This behavior was associated with the thermal desorption of H2 and the resultant formation of new dangling bond sites for H2O adsorption. For all temperatures, the oxidation kinetics of the chlorinated surface were nearly equivalent to the kinetics for the oxidation of clean silicon. This surprising result indicates that chlorine sites and free dangling bond sites react with equal probability to H2O. The kinetics of SiCl4 deposition were also measured on a Si(111)7×7 surface previously exposed to a saturation H2O dose. This chlorination reaction occurred at a much slower rate and was not as amenable to UHV studies.