Semiconductor device

A semiconductor device comprising:

• a substrate;
• an active pattern extending in a first direction on the substrate;
• a gate structure disposed on the active pattern and extending in a second direction different from the first direction;
• and
• a source/drain pattern filling a source/drain recess and formed on at least one side of the gate structure,
• wherein the source/drain pattern includes a first semiconductor pattern extending along the source/drain recess and contacting the active pattern, a second semiconductor pattern disposed on the first semiconductor pattern, a third semiconductor pattern disposed on the second semiconductor pattern, and a fourth semiconductor pattern that is disposed on the third semiconductor pattern and fills the source/drain recess,
• a side surface of the third semiconductor pattern, which is a boundary between the third semiconductor pattern and the second semiconductor pattern, includes an upper portion and a lower portion,
• a distance between the lower portion of the side surface of the third semiconductor pattern and the active pattern in the first direction is substantially constant, and
• a lower surface of the third semiconductor pattern includes a planar portion.

A semiconductor device comprising:

• an active pattern including a lower pattern and a plurality of sheet patterns disposed above the lower pattern and spaced apart from the lower pattern;
• a gate structure disposed on the lower pattern and surrounding the plurality of sheet patterns;
• and
• a source/drain pattern filling a source/drain recess and formed on at least one side of the gate structure,
• wherein the source/drain pattern includes a first semiconductor pattern extending along the source/drain recess and contacting the lower pattern, a second semiconductor pattern disposed on the first semiconductor pattern and extending along the first semiconductor pattern, a third semiconductor pattern disposed on the second semiconductor pattern and extending along the second semiconductor pattern, and a fourth semiconductor pattern that is disposed on the third semiconductor pattern and fills the source/drain recess,
• a lower surface of the third semiconductor pattern is disposed below a lower surface of a lowermost sheet pattern of the plurality of sheet patterns,
• a side surface of the third semiconductor pattern, which is a boundary between the third semiconductor pattern and the second semiconductor pattern, includes a first planar portion, and
• an upper surface of the fourth semiconductor pattern includes a second planar portion or an upwardly convex portion.