US Patent 9748386 Epitaxial structure of semiconductor device and manufacturing method thereof

An epitaxial structure of semiconductor device includes a substrate, a recess, a first epitaxial layer, a second epitaxial layer, and a third epitaxial layer. The recess is formed in the substrate and disposed near a surface of the substrate, wherein the recess has a recess depth. The first epitaxial layer is disposed on surfaces of a sidewall and a bottom of the recess. The second epitaxial layer is disposed on the surface of the first epitaxial layer, wherein the Ge concentration of the second epitaxial layer is greater than the Ge concentration of the first epitaxial layer. The third epitaxial layer is disposed on the surface of the second epitaxial layer, wherein the Ge concentration of the third epitaxial layer is greater than the Ge concentration of the second epitaxial layer, and the depth of the third epitaxial layer is about ½ to about ¾ of the recess depth.