Formation Mechanism of a Rounded SiGe-Etch-Front in an Isotropic Dry SiGe Etch Process for Gate-All-Around (GAA)-FETs

We investigated the formation mechanism of a rounded SiGe-etch-front (rounding), which causes low yield in GAA-FET manufacturing. The dependence on time of isotropic SiGe etching using NF3 plasma indicated that rounding was formed in the initial stage of the etch. The STEM-EDX results indicated that a Ge-containing surface layer, which was created in anisotropic patterning before isotropic etching, likely induced the rounding. The rounding amount was reduced by 33% using an improved anisotropic etch process.