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

Using alkaline chemistries for SiGe based Gate-All-Around architectures fabrication is still a challenge. This work reports a detailed study of Si to Si 0.7 Ge 0.3 selective etching using NH 4 OH, 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 SiO x + GeO x 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/Si 0.7 Ge 0.3 8 nm] × 2 superlattices, an anisotropic behavior toward Si (111) was noticed with Scanning Electron Microscopy. Only 6 nm (or <6 nm) 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 NH 4 OH alkaline chemistry reduced NH 4 OH anisotropy with respect to Si (111) planes, enabling the release of 10 nm wide SiGe nanowires without increasing the thickness of Si sacrificial layers.