FinFETs with Regrown Source/Drain and Methods for Forming the Same

A method comprising:

• forming a gate stack over a semiconductor substrate;
• etching the semiconductor substrate to form a recess in the semiconductor substrate, wherein the recess is adjacent to the gate stack, and wherein the semiconductor substrate has a first surface in the recess, with the first surface having a first roughness;
• after the step of etching the semiconductor substrate, removing a first surface layer of the semiconductor substrate to expose a second surface in the recess, wherein the first surface layer is in the recess, and wherein the second surface has a second roughness smaller than the first roughness;
• and
• performing an epitaxy to grow an epitaxy semiconductor region in the recess, wherein the epitaxy semiconductor region forms a source/drain region.

A method comprising:

• forming a gate dielectric over a semiconductor substrate;
• forming a gate electrode over the gate dielectric;
• forming a gate spacer on sidewalls of the gate dielectric and the gate electrode;
• etching the semiconductor substrate to form a recess in the semiconductor substrate, wherein the recess is etched using the gate spacer as an etching mask;
• performing a first reaction on a first surface layer of the semiconductor substrate to convert the first surface layer into a first reacted layer, wherein the first reacted layer is in the recess;
• removing the first reacted layer;
• and
• performing an epitaxy to grow a semiconductor material in the recess.