Atomic force microscopy on SiO2 layers grown on Ge implanted silicon

GexSi1-x layers were obtained by high dose Ge implants in (100) silicon substrates followed by solid phase epitaxy, Ge was implanted at several energies in the 35-140 keV range and for different doses ranging from 3 ?ó 1015/cm2 to 3 ?ó 1016/cm2. Atomic force; microscopy shows that surface roughness after oxidation is much larger in GexSi1-x samples than in silicon. Rutherford backscattering spectrometry reveals that the oxide layer formed on the GexSi1-x is essentially composed by SiO2, while Ge piles up at the SiO2/GexSi1-x interface. Ge accumulation is due to the selective oxidation of Si with respect to Ge, and produces Ge islands at the SiO2XGexSi1-x interface and the anomalous growth of the SiO2 layer. These effects are enhanced when thicker oxides are grown, or larger Ge doses are implanted, while they are reduced for implants at higher energies.