Cross-Hatch Related Oxidation and Its Impact on Performance of Strained-Si MOSFETs

The change in the morphology of thermally oxidized strained-Si layers on SiGe/Si substrates is studied using an atomic force microscope (AFM). The AFM observation was carried out before and after oxidation in an identical area of the sample. It was found that the oxidation rate of strained-Si was affected by the existence of the cross-hatch-related surface morphology. As the result, the surface roughness increased after oxidation. The roughness increase was more pronounced in a 30%-Ge-content sample than in a 15%-Ge-content sample. Strained-Si n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated and compared with unstrained Si devices. The enhancement of 58% of the transconductance was observed for the 15%-Ge-content wafer, while the 30%-Ge-content wafer exhibited a decrease of transconductance.