Method for fabricating semiconductor device
A method for fabricating semiconductor device includes the steps of: providing a substrate; forming a gate structure on the substrate; forming a spacer adjacent to the gate structure; forming a recess adjacent to the spacer; forming a buffer layer in the recess, wherein the buffer layer comprises a crescent moon shape; and forming an epitaxial layer on the buffer layer.
1. A method for fabricating semiconductor device, comprising:
providing a substrate;
forming a gate structure on the substrate;
forming a recess adjacent to the gate structure;
forming a buffer layer in the recess, wherein the buffer layer comprises a crescent moon shape, 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 comprises a completely curved surface; and
forming an epitaxial layer on the buffer layer.
2. The method of claim 1 , further comprising:
forming a spacer adjacent to the gate structure; and
forming the recess adjacent to the spacer.
3. The method 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 method of claim 3 , wherein the first width is between 3 nm to 7 nm.
5. The method of claim 3 , wherein the second width is between 5 nm to 9 nm.
6. The method of claim 1 , wherein a bottom surface of the epitaxial layer comprises a curve.
7. The method of claim 6 , wherein the buffer layer comprises a vertical thickness directly under a valley point of the curve.
8. The method of claim 7 , wherein the vertical thickness is between 7 nm to 11 nm.
9. The method of claim 1 , wherein a top surface of the epitaxial layer is even with a top surface of the substrate.
10. The method of claim 1 , wherein an etching to deposition ratio of the buffer layer is between 0.2 to 0.5.