| CPC H01L 29/78621 (2013.01) [H01L 21/823814 (2013.01); H01L 27/092 (2013.01); H01L 29/167 (2013.01); H01L 29/66553 (2013.01); H01L 29/66742 (2013.01); H01L 29/78696 (2013.01); H01L 29/0665 (2013.01); H01L 29/456 (2013.01)] | 20 Claims |

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1. A semiconductor structure, comprising:
a first pair of source/drain features;
a first stack of channel layers connected to the first pair of source/drain features;
a second pair of source/drain features; and
a second stack of channel layers connected to the second pair of source/drain features,
wherein the first pair of source/drain features each include a first epitaxial layer doped with a first dopant, a second epitaxial layer doped with a second dopant and disposed over the first epitaxial layer and connected to the first stack of channel layers, and a third epitaxial layer doped with a third dopant and disposed over the second epitaxial layer,
wherein the second pair of source/drain features each include a fourth epitaxial layer doped with a fourth dopant and connected to the second stack of channel layers, and a fifth epitaxial layer doped with a fifth dopant and disposed over the fourth epitaxial layer, and
wherein the first dopant, the second dopant, the third dopant, and the fourth dopant are of different species.
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