First Demonstration of 4-Stacked Ge0.915Sn0.085 Wide Nanosheets by Highly Selective Isotropic Dry Etching with High S/D Doping and Undoned Channels

The undoped stacked GeSn channels without parasitic Ge channels are realized by a radical-based highly selective isotropic dry etching. Heavily doped Ge sacrificial layers can reduce S/D resistance and the undoped GeSn channels can increase the channel mobility. SS=89m V /dec and $\mathrm{I}_{\mathrm{O}\mathrm{N}}=42\mu 1$ per stack ($10.5\mu A$. per sheet) at $\mathrm{V}_{\mathrm{OV}}\mathrm{V}_{\mathrm{DS}}=-0.5\mathrm{V}$ are achieved for the undoped 4-stacked 12nm-thick nanosheets with 120nm gate length and the width larger than 50nm. The etching selectivity and the channel uniformity are highly improved by the dry etching as compared to H202 wet etching. Both dry etching and undoped channel are essential to obtain stacked wide nanosheets with high performance.