Effect of SiO2 surface chemistry on the oxidation of silicon

We show that the retardation in the silicon oxidation rate associated with an ammonium hydroxide-hydrogen peroxide preclean is due to trace amounts of aluminum in the region of the SiO2 surface. This aluminum and the retarding effect can be eliminated by removing less than 50 Å of thermal oxide in a HF:H2O etch. Depositing thin films of aluminum with thicknesses between 0.05 and 1 monolayers (ML) on HF cleaned surfaces produced the same retardation as the NH4OH based cleans. These results indicate the importance of the SiO2 surface in silicon oxidation.