US Patent 10269655 Semiconductor device and method

An embodiment is a device including a first fin extending from a substrate, a first gate stack over and along sidewalls of the first fin, a first gate spacer disposed along a sidewall of the first gate stack, and a first epitaxial source/drain region in the first fin and adjacent the first gate spacer. The first epitaxial source/drain region including a first epitaxial layer on the first fin, the first epitaxial layer including silicon and carbon, a second epitaxial layer on the first epitaxial layer, the second epitaxial layer having a different material composition than the first epitaxial layer, the first epitaxial layer separating the second epitaxial layer from the first fin, and a third epitaxial layer on the second epitaxial layer, the third epitaxial layer having a different material composition than the first epitaxial layer.