Increase the volume of epitaxy regions
A method includes forming a gate stack on a plurality of semiconductor fins. The plurality of semiconductor fins includes a plurality of inner fins, and a first outer fin and a second outer fin on opposite sides of the plurality of inner fins. Epitaxy regions are grown based on the plurality of semiconductor fins, and a first height of the epitaxy regions measured along an outer sidewall of the first outer fin is smaller than a second height of the epitaxy regions measured along an inner sidewall of the first outer fin.
1. A method comprising:
forming isolation regions over a bulk semiconductor substrate;
recessing the isolation regions, wherein top portions of semiconductor strips between the isolation regions protrude higher than top surfaces of the isolation regions to form a fin group, and the fin group comprising:
a plurality of inner fins; and
a first outer fin and a second outer fin on opposite sides of the plurality of inner fins;
forming fin spacers on sidewalls of the plurality of inner fins, the first outer fin, and the second outer fin, wherein the fin spacers comprise:
an outer fin spacer on an outer sidewall of the first outer fin, wherein the outer sidewall faces away from the fin group, and the outer fin spacer has a first height; and
an inner fin spacer on an inner sidewall of the first outer fin, wherein the inner sidewall faces toward the plurality of inner fins, and the inner fin spacer has a second height smaller than the first height; and
epitaxially growing epitaxy regions based on the plurality of inner fins, the first outer fin, and the second outer fin, wherein the epitaxially growing epitaxy regions comprises pulsing a bias voltage with a plurality of cycles.
2. The method of claim 1 , wherein the first height is greater than the second height by a height difference greater than about 2 nm.
3. The method of claim 1 , wherein the outer fin spacer and the inner fin spacer are formed in a common process.
4. The method of claim 1 further comprising forming a gate stack, wherein the gate stack extends on sidewalls and a top surface of each of the plurality of inner fins, the first outer fin, and the second outer fin.
5. The method of claim 4 further comprising forming a gate spacer on sidewalls of the gate stack, wherein the gate spacer and the fin spacers are formed in a common formation process.
6. The method of claim 1 , wherein a third height of the epitaxy regions measured directly over the outer fin spacer is smaller than a fourth height of the epitaxy regions measured directly over the inner fin spacer.
7. The method of claim 6 , wherein the fourth height is greater than the third height by a height difference greater than about 2 nm.
8. The method of claim 1 , wherein the pulsing has a duty cycle in a range between about 10 percent and about 90 percent.
9. A method comprising:
forming isolation regions extending into a semiconductor substrate;
forming a plurality of semiconductor fins protruding higher than the isolation regions, wherein the plurality of semiconductor fins comprise:
a plurality of inner fins; and
a first outer fin and a second outer fin on opposite sides of the plurality of inner fins;
forming fin spacers on sidewalls of the plurality of semiconductor fins, wherein the forming the fin spacers comprises:
depositing a spacer layer on top surfaces and sidewalls of the plurality of semiconductor fins;
performing a first etching process to thin the spacer layer;
removing a first polymer generated in the first etching process;
after the first polymer is removed, performing a second etching process to etch the spacer layer; and
removing a second polymer generated in the second etching process, and wherein the fin spacers comprise:
a first outer fin spacer and a second outer fin spacer having a third height, wherein the first outer fin spacer is vertical, and comprises an inner sidewall contacting the first outer fin, and an outer sidewall opposing the inner sidewall, wherein each of the inner sidewall and the outer sidewall extends to contact a top surface of a portion of the isolation regions; and
an inner fin spacer between the first outer fin spacer and the second outer fin spacer, wherein the inner fin spacer has a fourth height smaller than the third height; and
epitaxially growing epitaxy regions based on the plurality of semiconductor fins, wherein a first height of the epitaxy regions measured along an outer sidewall of the first outer fin is smaller than a second height of the epitaxy regions measured along the inner sidewall of the first outer fin.
10. The method of claim 9 , wherein a difference between the first height and the second height is greater than about 2 nm.
11. The method of claim 9 , wherein the epitaxy regions formed based on the plurality of semiconductor fins is merged.
12. The method of claim 9 , wherein the epitaxy regions formed based on the plurality of semiconductor fins is un-merged.
13. The method of claim 10 , wherein a difference between the third height and the fourth height is greater than about 2 nm.
14. The method of claim 9 further comprising, before the epitaxially growing epitaxy regions, recessing the plurality of semiconductor fins to form recesses, wherein bottoms of the recesses are lower than bottoms of the isolation regions.
15. A method comprising:
depositing a spacer layer on top surfaces and sidewalls of a plurality of protruding fins, wherein the plurality of protruding fins comprise:
a plurality of inner fins; and
a first outer fin and a second outer fin on opposing sides the plurality of inner fins;
etching the spacer layer to form fin spacers on sidewalls of the plurality of protruding fins, wherein the fin spacers comprise:
a first fin spacer on a first sidewall of the first outer fin, wherein the first fin spacer has a first height; and
a second fin spacer on a second sidewall of the first outer fin, wherein the second fin spacer has a second height smaller than the first height, wherein the etching the spacer layer comprises performing a plurality of cycles, each comprising:
performing an etching process to etch the spacer layer; and
after the etching process, removing a polymer generated in the etching process.
16. The method of claim 15 , wherein the first sidewall faces away from the plurality of protruding fins, and the second sidewall faces toward the plurality of inner fins.
17. The method of claim 15 , wherein the first height is greater than the second height by a height difference greater than about 2 nm.
18. The method of claim 15 , wherein the first fin spacer and the second fin spacer are formed in a same etching process.
19. The method of claim 15 further comprising forming a gate stack on the plurality of protruding fins.
20. The method of claim 15 , wherein at a time the etching the spacer layer is started, a portion of the spacer layer covers a portion of an isolation region, and the portion of the spacer layer extends from the first outer fin to a third outer fin, and wherein at the time, all top surfaces of the portion of the spacer layer are exposed to a corresponding etching chemical used for the etching the spacer layer.