Wet Alkaline Etching of Si Selectively to SiGe for sub 10 nm Gate All Around Architectures

Abstract

Using alkaline chemistries for SiGe stacked nanowires fabrication is still a challenge. This work reports a detailed study of Si to Si0.7Ge0.3 selective etching using NH4OH, TMAH and TEAH alkaline etchants. These alkaline solutions have all shown a great selectivity with respect to SiGe (up to 300). X-ray Photoelectron Spectroscopy and Atomic Force Microscopy have evidenced the presence of a smooth mix of SiOx + GeOx oxides during SiGe alkaline etching, which explains the obtained selectivity. When such alkaline etching processes were used on wafers with mesas etched in [Si 8 nm / Si0.7Ge0.3 8 nm] × 2 superlattices, an anisotropic behavior toward Si (111) was noticed with Scanning Electron Microscopy. Only 6 nm (or < 6nm) wide devices could be fabricated with the studied alkaline chemistries. Releasing wider SiGe nanowires required greater Si sacrificial layers' thicknesses than √2 Critical Dimension. Finally, addition of peroxide to NH4OH alkaline chemistry reduced NH4OH anisotropy with respect to Si (111) planes, enabling the release of 10 nm wide SiGe nanowires without increasing the thickness of Si sacrificial layers.