Semiconductor device and method for fabricating the same
A method for fabricating semiconductor device is disclosed. First, a substrate is provided, a gate structure is formed on the substrate, a recess is formed adjacent to the gate structure, a buffer layer is formed in the recess, and an epitaxial layer is formed on the buffer layer. Preferably, the buffer layer includes a crescent moon shape.
1. A semiconductor device, comprising:
a substrate;
a gate structure on the substrate;
a buffer layer adjacent to the gate structure, wherein the buffer layer comprises a crescent moon shape and the buffer layer comprises an inner curve and an outer curve intersect on a top surface of the substrate, and each of the inner curve and the outer curve intersect on the top surface of the substrate comprises a completely curved surface; and
an epitaxial layer on the buffer layer.
2. The semiconductor device of claim 1 , further comprising:
a spacer adjacent to the gate structure; and
the buffer layer adjacent to the spacer.
3. The semiconductor device of claim 2 , wherein the buffer layer comprises a first width and a second width directly under the spacer, wherein the second width is greater than the first width.
4. The semiconductor device of claim 3 , wherein the first width is between 3 nm to 7 nm.
5. The semiconductor device of claim 3 , wherein the second width is between 5 nm to 9 nm.
6. The semiconductor device of claim 1 , wherein a bottom surface of the epitaxial layer comprises a curve.
7. The semiconductor device of claim 6 , wherein the buffer layer comprises a vertical thickness directly under a valley point of the curve.
8. The semiconductor device of claim 7 , wherein the vertical thickness is between 7 nm to 11 nm.
9. The semiconductor device of claim 1 , wherein a top surface of the epitaxial layer is even with a top surface of the substrate.