Semiconductor device and method

A device comprising:

• a fin extending upwards from a substrate;
• a gate electrode over the fin;
• and
• an epitaxial source/drain region in the fin, the epitaxial source/drain region comprising:
• a first epitaxial region on the fin, the first epitaxial region comprising silicon and carbon;
• a second epitaxial region on the first epitaxial region, wherein the second epitaxial region has a different material composition than the first epitaxial region, and wherein the first epitaxial region is interposed between the second epitaxial region and the fin;
• and
• a third epitaxial region on the second epitaxial region, wherein the third epitaxial region has a different material composition than both the first epitaxial region and the second epitaxial region.

A device comprising:

• a semiconductor fin;
• a gate stack extending on a top surface and sidewalls of the semiconductor fin;
• a gate spacer extending on a sidewall of the gate stack;
• and
• a source/drain region in the semiconductor fin and adjacent the gate spacer, the source/drain region comprising:
• a first source/drain region on the semiconductor fin;
• a second source/drain region on the first source/drain region, the first source/drain region separating the second source/drain region from the semiconductor fin;
• and
• a third source/drain region on the second source/drain region, the first source/drain region having a greater concentration of carbon than the second source/drain region and the third source/drain region.