Transistor with buried silicon germanium for improved proximity control and optimized recess shape

A method of forming a semiconductor device comprising:

• providing a substrate including a semiconductor layer on a germanium-containing silicon layer, wherein a base semiconductor layer is present underlying the germanium-containing silicon layer;
• forming a gate structure on a surface of a channel portion of the semiconductor layer of the substrate;
• etching well trenches into the substrate on opposing sides of the gate structure by removing the entirety of said semiconductor layer on opposing sides of the gate structure and a portion of the underlying germanium-containing silicon layer, wherein said etching provides a recess in said germanium-containing silicon layer;
• conducting a second etch step comprising an undercut etch that is selective to the (111) facet of the semiconductor layer and is selective to the recessed germanium-containing silicon layer, wherein the second step is a wet etch using tetramethylammonium hydroxide (TMAH);
• removing remaining portions of the recessed germanium-containing silicon layer located on opposing sides of the gate structure to expose a portion of the base semiconductor layer, while keeping a remaining portion of the germanium-containing silicon layer under the gate structure untouched;
• and
• epitaxially growing a stress inducing semiconductor material in direct contact with the portion of the base semiconductor layer that is exposed to fill at least a portion of each well trench to provide at least one of a stress inducing source region and a stress inducing drain region having a planar base.