CPC H01L 29/0847 (2013.01) [H01L 21/02532 (2013.01); H01L 29/66545 (2013.01); H01L 29/6681 (2013.01); H01L 29/785 (2013.01)] | 20 Claims |
1. A device comprising:
a fin extending from a substrate;
a gate stack over the fin;
a source/drain region in the fin adjacent the gate stack, the source/drain region comprising:
a first source/drain layer having a germanium concentration of that is lower than 40 atomic percent and having a thickness of less than 10 nm;
a second source/drain layer over the first source/drain layer, the second source/drain layer having a germanium concentration of 40 to 50 atomic percent and having a thickness that is less than 25 nm;
a third source/drain layer over the second source/drain layer, the third source/drain layer having a germanium concentration of 60 to 80 atomic percent;
a fourth source/drain layer over the third source/drain layer, the fourth source/drain layer having a germanium concentration that is less than 40 atomic percent, wherein each of the first source/drain layer, the second source/drain layer, the third source/drain layer and the fourth source/drain layer comprise facets, and wherein a topmost point of the first source/drain layer is lower than a bottommost point of the third source/drain layer and a bottommost point of the fourth source/drain layer; and
a source/drain contact contacting the source/drain region.
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