Characterization of ultrathin SOI film and application to short channel MOSFETs

Abstract

In this study, a very dilute solution(NH4OH:H2O2:H2O 1:8:64 mixture) was employed to reduce the thickness of commerciallyavailable SOI wafers down to 3 nm. The etch rate is precisely controlled at0.11 Å s−1 based on the self-limited etching speed of the solution. The thickness uniformity of the thinfilm, evaluated by spectroscopic ellipsometry and by high-resolution x-ray reflectivity,remains constant through the thinning process. Moreover, the film roughness, analyzed byatomic force microscopy, slightly improves during the thinning process. The residual stressin 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 significantlyreduced compared to the value of bulk silicon. Finally, the thinned SOI waferswere used to fabricate Schottky-barrier metal-oxide-semiconductor field-effecttransistors with a gate length down to 30 nm, featuring state-of-the-art current driveperformance.