Method for manufacturing FinFET structure with doped region

1. A method for forming a semiconductor structure, comprising:

forming a fin structure over a substrate;

forming a gate structure across the fin structure;

forming a fin spacer on a sidewall of the fin structure;

partially removing the fin spacer;

recessing the fin structure to form a recess;

implanting dopants from the recess to form a doped region;

diffusing the dopants in the doped region to form an expanded doped region; and

forming a source/drain structure over the expanded doped region.

2. The method for forming a semiconductor structure as claimed in claim 1 , wherein a ratio of a depth of the recess to a thickness of the expanded doped region is in a range from about 0.6 to about 1.2.

3. The method for forming a semiconductor structure as claimed in claim 1 , wherein a depth of the recess in the fin structure is in a range from about 15 nm to about 35 nm.

4. The method for forming a semiconductor structure as claimed in claim 1 , further comprising:

forming a gate spacer on a sidewall of the gate structure,

wherein an edge of the doped region is located directly under the gate spacer and an edge of the expanded doped region is located directly under the gate structure.

5. The method for forming a semiconductor structure as claimed in claim 1 , wherein the expanded doped region is in direct contact with a sidewall and a bottom surface of the source/drain structure.

6. The method for forming a semiconductor structure as claimed in claim 1 , wherein the fin spacer has a sloping top surface after partially removing the fin spacer.

7. The method for forming a semiconductor structure as claimed in claim 6 , wherein the fin spacer has a first height closer to the gate structure and a second height away from the gate structure, and the first height is greater than the second height.

8. The method for forming a semiconductor structure as claimed in claim 1 , wherein the dopants in the doped region comprises germanium, boron, phosphorous, arsenic, or antimony.

9. A method for forming a semiconductor structure, comprising:

forming a fin structure over a substrate;

forming an isolation structure around the fin structure;

forming a gate structure across the fin structure and extending over the isolation structure;

forming a gate spacer on a sidewall of the gate structure;

etching the fin structure to form a recess;

implanting first dopants from the recess to form a doped region, wherein a first edge of the doped region is located under the gate spacer;

diffusing the first dopants to form an expanded doped region, wherein a second edge of the expanded doped region is located under the gate structure; and

forming a source/drain structure in the recess.

10. The method for forming a semiconductor structure as claimed in claim 9 , wherein a distance between the first edge of the doped region and the second edge of the expanded doped region is in a range from about 3 nm to about 9 nm.

11. The method for forming a semiconductor structure as claimed in claim 9 , wherein a distance between the first edge of the doped region and the second edge the expanded doped region is smaller than a distance between a bottom edge of the doped region and a bottom edge of the expanded doped region.

12. The method for forming a semiconductor structure as claimed in claim 9 , wherein an annealing process is performed at a temperature in a range from about 500° C. to about 700° C. to form the expanded doped region.

13. The method for forming a semiconductor structure as claimed in claim 9 , wherein a bottommost portion of the recess is higher than a top surface of the isolation structure.

14. The method for forming a semiconductor structure as claimed in claim 1 , wherein a ratio of a depth of the recess to a thickness of the expanded doped region is in a range from about 0.6 to about 1.2.

15. A method for forming a semiconductor structure, comprising:

forming a first fin structure over a substrate;

forming an isolation structure around the first fin structure;

forming a gate structure across the first fin structure and extending over the isolation structure;

forming a first fin spacer on a sidewall of the first fin structure;

etching the first fin spacer to form a first sloping top surface;

etching the first fin structure to form a first recess having a second sloping top surface;

implanting first dopants in the first fin structure to form a first doped region;

annealing the first doped region to form a first expanded doped region; and

forming a source/drain structure over the first expanded doped region.

16. The method for forming a semiconductor structure as claimed in claim 15 , wherein the first sloping top surface of the first fin spacer is higher than the second sloping top surface of the first recess.

17. The method for forming a semiconductor structure as claimed in claim 15 , wherein the second sloping top surface of the first fin structure is higher than a top surface of the isolation structure.

18. The method for forming a semiconductor structure as claimed in claim 15 , wherein a bottommost portion of the first expanded doped region is lower than a top surface of the isolation structure.

19. The method for forming a semiconductor structure as claimed in claim 15 , further comprising:

forming a second fin structure over the substrate;

forming a second fin spacer on a sidewall of the second fin structure;

etching the second fin spacer to form a second sloping top surface;

etching the second fin structure to form a second recess;

implanting the first dopants in the second fin structure to form a second doped region; and

annealing the second doped region to form a second expanded doped region, wherein the source/drain structure further extends over the second expanded doped region.

20. The method for forming a semiconductor structure as claimed in claim 19 , wherein the source/drain structure is in direct contact with both the first extended doped region and the second extended doped region.