Thermal decomposition of ultrathin oxide layers on Si(100)

Decomposition of ultrathin oxide layers on Si(100) has been studied using isothermal desorption, temperature programmed desorption and readsorption on partially desorbed layers using isotopically labeled oxygen. We find that inhomogeneous decomposition, with void formation in which clean silicon is exposed, occurs at coverages as low as 0.3 monolayers. Whereas the activation energy for SiO(g) formation is essentially independent of coverage between 10−3 and 10 monolayers, the apparent preexponential factor decreases substantially with increasing coverage. The discrepancy between the kinetic parameters measured for SiO(g) production in modulated molecular beam experiments and those measured using temperature programmed desorption is attributed to a strong decrease in the rate constant for desorption of SiO(g) with increasing coverage. Both methods give similar results at nearly identical coverages.