Fin field effect transistor (FinFET) device and method for forming the same

1. A fin field effect transistor (FinFET) device structure, comprising:

a substrate;

a fin structure extending above the substrate;

an epitaxial structure formed on the fin structure, wherein the epitaxial structure has a first height, and the epitaxial structure comprises a rhombus-like upper portion and a column-like lower portion;

fin sidewall spacers formed adjacent to the epitaxial structure, wherein the fin sidewall spacers have a second height and the first height is greater than the second height, and wherein the rhombus-like upper portion is entirely above a top of the fin sidewall spacers, and a junction between the rhombus-like upper portion and the sidewall of the column-like lower portion is higher than a peak of the fin sidewall spacers, and a bottom surface of the column-like lower portion is leveled with a bottom surface of the fin sidewall spacers.

2. The fin field effect transistor (FinFET) device structure as claimed in claim 1 , further comprising:

a gate stack structure is formed over a central portion of the fin structure, wherein the epitaxial structure formed adjacent to the central portion of the fin structure.

3. The fin field effect transistor (FinFET) device structure as claimed in claim 1 , wherein the second height is in a range from about 0.1 nm to about 100 nm.

4. The fin field effect transistor (FinFET) device structure as claimed in claim 1 , further comprising:

an isolation structure, wherein the fin structure is embedded in the isolation structure.

5. The fin field effect transistor (FinFET) device structure as claimed in claim 4 , wherein a bottom surface of the epitaxial structure is level with a top surface of the isolation structure.

6. The fin field effect transistor (FinFET) device structure as claimed in claim 1 , wherein the epitaxial structure extends from the top surface of the isolation structure to a depth in a range from about 0.1 nm to about 50 nm.

7. The fin field effect transistor (FinFET) device structure as claimed m claim 1 , wherein the epitaxial structure comprises a source/drain structure.

8. The fin field effect transistor (FinFET) device structure as claimed in claim 1 , wherein the column-like lower portion has a bottom surface and sidewalls adjoined to the bottom surface and an angle between the bottom surface and the sidewalls is about 90 degrees.

9. A fin field effect transistor (FinFET) device structure, comprising:

a substrate;

a fin structure extending above the substrate;

an isolation structure formed on the substrate, wherein the fin structure is embedded in the isolation structure;

a first epitaxial structure formed on the fin structure, wherein the first epitaxial structure comprises a rhombus-like upper portion and a column-like lower portion, the column-like lower portion has a bottom surface and a sidewall adjoined to the bottom surface, an angle between the bottom surface and the sidewall is about 90 degrees, a junction between the rhombus-like upper portion and the sidewall of the column-like lower portion is above the top surface of the isolation structure such that the rhombus-like upper portion is entirely located above the top surface of the isolation structure; and

fin sidewall spacers formed adjacent to the first epitaxial structure, wherein a peak of the fin sidewall spacers is higher than a bottom surface of the column-like lower portion and lower than the junction.

10. The fin field effect transistor (FinFET) device structure as claimed in claim 9 , wherein the first epitaxial structure extends from the top surface of the isolation structure to a depth in a range from about 0.1 nm to about 50 nm.

11. The fin field effect transistor (FinFET) device structure as claimed in claim 9 , further comprising:

a gate stack structure is formed over a central portion of the fin structure; and gate sidewall spacers formed adjacent to the gate stack structure.

12. The fin field effect transistor (FinFET) device structure as claimed in claim 9 , further comprising:

a second epitaxial structure adjacent to the first epitaxial structure, wherein a spacing between the first epitaxial structure and the second epitaxial structure is in a range from about 0.1 nm to about 100 nm.

13. The fin field effect transistor (FinFET) device structure as claimed in claim 9 , wherein the rhombus-like upper portion has four facets, each of the four facets has a (111) crystallographic orientation, two of the four facets joining the sidewall of the column-like lower portion, and the four facets are entirely located above the top surface of the isolation structure.

14. The fin field effect transistor (FinFET) device structure as claimed in claim 9 , wherein the fin structure has a first width, the first epitaxial structure has a second width and the second width is greater than the first width.

15. The fin field effect transistor (FinFET) device structure as claimed in claim 1 , wherein the first height is in a range from about 10 nm to about 300 nm, and the epitaxial structure has a first width in a range from about 10 nm to about 100 nm.

16. The fin field effect transistor (FinFET) device structure as claimed in claim 1 , wherein a ratio of the first height to the second height is in a range from about 1.5 to about 10.

17. The fin field effect transistor (FinFET) device structure as claimed in claim 1 , wherein the lattice constants of the epitaxial structure are different from that of the substrate.

18. The fin field effect transistor (FinFET) device structure as claimed in claim 9 , wherein the first epitaxial structure has a height in a range from about 10 nm to about 300 nm and a width in a range from about 10 nm to about 100 nm.

19. The fin field effect transistor (FinFET) device structure as claimed in claim 9 , wherein a ratio of the height to the width of the first epitaxial structure is in a range from about 0.1 to about 10.