Semiconductor device including source/drain pattern with main layer and buffer layer having germanium and method of fabricating the same

A semiconductor device, comprising:

• a substrate comprising an n-type metal-oxide-semiconductor (MOS) field-effect transistor (FET) (NMOSFET) region;
• an active pattern on the NMOSFET region;
• a channel pattern on the active pattern, the channel pattern comprising a plurality of semiconductor patterns spaced apart from each other;
• a source/drain pattern on the active pattern;
• a gate electrode on the channel pattern, the gate electrode comprising:
• an inner electrode between adjacent semiconductor patterns of the plurality of semiconductor patterns;
• and
• an outer electrode on a uppermost semiconductor pattern of the plurality of semiconductor patterns;
• a gate insulating layer between the gate electrode and each of the plurality of semiconductor patterns;
• a gate spacer on a side surface of the outer electrode;
• a gate capping pattern on a top surface of the outer electrode;
• an interlayer insulating layer on the gate capping pattern and the source/drain pattern;
• a gate contact penetrating the interlayer insulating layer and the gate capping pattern, the gate contact connected to the gate electrode;
• an active contact penetrating the interlayer insulating layer and connected to the source/drain pattern;
• a first metal layer on the interlayer insulating layer, the first metal layer comprising a plurality of first interconnection lines respectively connected to the gate contact and the active contact;
• and
• a second metal layer on the first metal layer,
• wherein the second metal layer comprises a plurality of second interconnection lines connected to the first metal layer,
• wherein the source/drain pattern comprises a buffer layer and a main layer on the buffer layer,
• wherein the main layer comprises an upper portion comprising at least one facet surface,
• wherein the at least one facet surface is a {111} plane, and
• wherein the buffer layer at least partially covers the at least one facet surface.