Characterization of ultrathin SOI film and application to short channel MOSFETs

In this study, a very dilute solution (NHOH:HO :HO 1:8:64 mixture) was employed to reduce the thickness of commercially available SOI wafers down to 3 nm. The etch rate is precisely controlled at 0.11 Å s based on the self-limited etching speed of the solution. The thickness uniformity of the thin film, evaluated by spectroscopic ellipsometry and by high-resolution x-ray reflectivity, remains constant through the thinning process. Moreover, the film roughness, analyzed by atomic force microscopy, slightly improves during the thinning process. The residual stress in the thin film is much smaller than that obtained by sacrificial oxidation. Mobility, measured by means of a bridge-type Hall bar on 15 nm film, is not significantly reduced compared to the value of bulk silicon. Finally, the thinned SOI wafers were used to fabricate Schottky-barrier metal-oxide-semiconductor field-effect transistors with a gate length down to 30 nm, featuring state-of-the-art current drive performance.