Semiconductor device and fabrication method thereof

A fabrication method of a semiconductor device, comprising:

• providing a substrate having a fin, wherein the fin has a plurality of first fin layers stacked along a normal direction of a substrate surface and a second fin layer between two adjacent first fin layers;
• forming a dummy gate structure across the fin, wherein the dummy gate structure covers a portion of a top surface and sidewall surfaces of the fin;
• after forming the dummy gate structure, respectively forming a first groove and a second groove in the fin on two sides of the dummy gate structure;
• removing a portion of the second fin layer adjacent to the first groove to form a first fin recess between two adjacent first fin layers;
• removing a portion of the second fin layer adjacent to the second groove to form a second fin recess between two adjacent first fin layers, wherein a size of the first fin recess along an extending direction of the fin is greater than a size of the second fin recess along the extending direction of the fin;
• forming a first spacer layer in the first fin recess, wherein sidewalls of the first spacer layer are coplanar with sidewalls of the first fin layer exposed by the first groove;
• forming a second spacer layer in the second fin recess, wherein sidewalls of the second spacer layer are coplanar with sidewalls of the first fin layer exposed by the first groove;
• after forming the first spacer layer, forming a doped drain layer in the first groove;
• and
• after forming the second spacer layer, forming a doped source layer in the second groove.