SIMS investigation of the Si(111) oxidation promoted by potassium overlayers

The removal of the potassium is a critical issue in the Si oxidation promoted by potassium overlayers. The effects of the morphology of the potassium and SiO2 overlayers on the potassium desorption process have been investigated using a very sensitive technique: SIMS. For a uniform potassium overlayer (monolayer, simultaneous oxygen/potassium adsorption or multilayers exposed to low O2 pressure) there is no evidence of a significant amount of potassium left after its desorption. However, under specific conditions: potassium multilayers exposed to high O2 pressure (in which SiO2 islands were observed using SEM), there is a significant amount of potassium left under the surface after the desorption attempt. These effects of the overlayer morphologies allow us to explain some reported contradictory results.