ATOMIC-FORCE MICROSCOPY ON SIO2 LAYERS GROWN ON GE IMPLANTED SILICON

GexSi1-x layers were obtained by high dose Ge implants in (100) silico n substrates followed by solid phase epitaxy. Ge was implanted at seve ral energies in the 35-140 keV range and for different doses ranging f rom 3 x 10(15)/cm(2) to 3 x 10(16)/cm(2). Atomic force microscopy show s that surface roughness after oxidation is much larger in GexSi1-x sa mples 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 accumulati on is due to the selective oxidation of Si with respect to Ge, and pro duces Ge islands at the SiO2/GexSi1-x interface and the anomalous grow th of the SiO2 layer. These effects are enhanced when thicker oxides a re grown, or larger Ge doses are implanted, while they are reduced for implants at higher energies.