Method of manufacturing a semiconductor device and a semiconductor device

A semiconductor device comprising:

• a fin structure disposed over a substrate;
• a gate structure disposed over a part of the fin structure;
• and
• a source/drain epitaxial layer over a source/drain region of the fin structure, wherein:
• an interface between the source/drain epitaxial layer and the source/drain region of the fin structure has a W-shape having two deeper portions and one shallow portion disposed between the two deeper portions, the shallow portion having a smaller depth than the deeper portions.

A semiconductor device comprising:

• a semiconductor layer having a channel region;
• a gate structure disposed over the channel region;
• and
• a source/drain epitaxial layer over a source/drain region of the semiconductor layer, wherein:
• an interface between the source/drain epitaxial layer and the source/drain region has a W-shape having two deeper portions and one shallow portion disposed between the two deeper portions, the shallow portion having a smaller depth than the deeper portions, and
• when G1 is a thickness of the source/drain epitaxial layer corresponding to the shallow portion and G2 is a thickness of the source/drain epitaxial layer corresponding to one of the deeper portions, G1/G2 is in a range from 0.9 to 1.05.