Semiconductor device

A semiconductor device comprising:

• an active pattern that includes a lower pattern extending in a first direction, and a plurality of sheet patterns spaced apart from the lower pattern in a second direction perpendicular to the first direction;
• a plurality of gate structures that are on the lower pattern and spaced apart from each other in the first direction, and include a gate electrode and a gate insulating film;
• and
• a source/drain pattern between adjacent ones of the gate structures,
• wherein the source/drain pattern includes a semiconductor liner film in contact with the lower pattern and the sheet patterns, a lower semiconductor filling film on the semiconductor liner film, an upper semiconductor filling film on the lower semiconductor filling film, and a semiconductor buffer film between the lower semiconductor filling film and the upper semiconductor filling film,
• wherein the semiconductor liner film, the lower semiconductor filling film, the upper semiconductor filling film, and the semiconductor buffer film each include silicon-germanium,
• wherein a germanium fraction of the semiconductor buffer film is smaller than a germanium fraction of the upper semiconductor filling film and a germanium fraction of the lower semiconductor filling film,
• wherein the semiconductor buffer film extends along a profile of a lower filling film recess defined by the lower semiconductor filling film,
• wherein the semiconductor buffer film includes a bottom portion, and a side portion extending in the second direction from the bottom portion, and
• wherein a germanium fraction of the side portion is different from a germanium fraction of the bottom portion.

A semiconductor device comprising:

• an active pattern that includes a lower pattern extending in a first direction, and a plurality of sheet patterns spaced apart from the lower pattern in a second direction perpendicular to the first direction;
• a plurality of gate structures that are on the lower pattern and spaced apart from each other in the first direction, and include a gate electrode and a gate insulating film;
• and
• a source/drain pattern between adjacent ones of the gate structures,
• wherein the source/drain pattern includes a semiconductor liner film in contact with the lower pattern and the sheet patterns, a lower semiconductor filling film on the semiconductor liner film, an upper semiconductor filling film on the lower semiconductor filling film, and a semiconductor buffer film between the lower semiconductor filling film and the upper semiconductor filling film,
• wherein the semiconductor liner film, the lower semiconductor filling film, the upper semiconductor filling film, and the semiconductor buffer film each include silicon-germanium,
• wherein a germanium fraction of the semiconductor buffer film is smaller than a germanium fraction of the upper semiconductor filling film and a germanium fraction of the lower semiconductor filling film,
• wherein the semiconductor buffer film extends along a profile of a lower filling film recess defined by the lower semiconductor filling film,
• wherein the semiconductor buffer film includes a bottom portion, and a side portion extending in the second direction from the bottom portion, and
• wherein a thickness of the side portion is greater than a thickness of the bottom portion.