Semiconductor device and method

1. A method comprising:

forming a first gate stack on a first semiconductor fin and a second gate stack on a second semiconductor fin, the first semiconductor fin and the second semiconductor fin protruding above an isolation region;

depositing a spacer layer on the first gate stack, the second gate stack, the first semiconductor fin, the second semiconductor fin, and the isolation region;

forming a mask on the spacer layer, the mask covering the second semiconductor fin, the first semiconductor fin uncovered by the mask;

implanting a first dopant having a first doping type in the spacer layer over the first semiconductor fin while the mask shields the spacer layer over the second semiconductor fin;

performing an anneal process to drive the first dopant from the spacer layer into the first semiconductor fin and the isolation region, wherein the spacer layer covers the first semiconductor fin and the isolation region during the anneal process; and

after performing the anneal process, patterning the spacer layer to form a first gate spacer and a second gate spacer, the first gate spacer extending along a sidewall of the first gate stack, the second gate spacer extending along a sidewall of the second gate stack.

2. The method of claim 1 further comprising:

after patterning the spacer layer, forming a third gate spacer and a fourth gate spacer, the third gate spacer extending along a sidewall of the first gate spacer, the fourth gate spacer extending along a sidewall of the second gate spacer.

3. The method of claim 1 further comprising:

forming a source/drain region in the first semiconductor fin, the source/drain region having the first doping type.

4. The method of claim 1 , wherein the first gate stack is formed on a channel region of the first semiconductor fin, the channel region being free of the first dopant after performing the anneal process.

5. The method of claim 4 , wherein driving the first dopant into the first semiconductor fin forms a lightly doped drain/source region in the first semiconductor fin, the lightly doped drain/source region partially disposed under the channel region.

6. The method of claim 1 , wherein after performing the anneal process, a concentration of the first dopant in the isolation region decreases in a direction extending from a top of the isolation region to a bottom of the isolation region.

7. The method of claim 1 , wherein implanting the first dopant in the spacer layer comprises:

depositing a layer of the first dopant on the spacer layer during a discharge pulse of a plasma doping process; and

driving the first dopant into the spacer layer during an implant pulse of the plasma doping process.

8. The method of claim 7 further comprising:

removing the mask and the layer of the first dopant with a wet etch process, wherein the wet etch process does not remove the first dopant from the spacer layer.

9. A method comprising:

depositing a dielectric layer on a semiconductor fin and an isolation region, the semiconductor fin protruding above the isolation region;

performing a plasma doping process comprising:

depositing a layer of a first dopant on the dielectric layer during a discharge pulse of the plasma doping process; and

implanting particles of the first dopant into the dielectric layer during an implant pulse of the plasma doping process;

removing the layer of the first dopant with an etch process, wherein the etch process does not remove the particles of the first dopant implanted into the dielectric layer; and

performing a thermal anneal process to drive the particles of the first dopant from the dielectric layer into the semiconductor fin and the isolation region, wherein the dielectric layer covers the semiconductor fin and the isolation region during the thermal anneal process.

10. The method of claim 9 , wherein the discharge pulse comprises generating a plasma from a precursor for the first dopant, and the implant pulse comprises accelerating the particles of the first dopant across the plasma.

11. The method of claim 10 , wherein the precursor for the first dopant is B 2 H 6 .

12. The method of claim 9 , wherein the particles of the first dopant are implanted with an implantation energy in a range of 0.1 KV to 3 KV.

13. The method of claim 9 , wherein a dosage of the first dopant during the implant pulse is in a range of 1E15 atoms/cm 3 to 5E16 atoms/cm 3 .

14. The method of claim 9 , wherein the etch process comprises a wet etch performed using an acid comprising H 2 SO 4 and H 2 O 2 .

15. The method of claim 9 , wherein the thermal anneal process is performed in an environment comprising oxygen and nitrogen.

16. The method of claim 9 , wherein after performing the thermal anneal process, a concentration of the first dopant in the isolation region decreases in a direction extending from a top of the isolation region to a bottom of the isolation region.

17. The method of claim 9 further comprising:

patterning the dielectric layer to form a spacer on the semiconductor fin.

18. A method comprising:

forming a gate stack on a semiconductor fin, the semiconductor fin protruding above an isolation region;

depositing an insulating layer on the gate stack, the semiconductor fin, and the isolation region;

implanting a dopant having a first doping type in the insulating layer;

forming a lightly doped drain/source region in the semiconductor fin by driving the dopant from the insulating layer into the semiconductor fin and the isolation region while the insulating layer covers the semiconductor fin and the isolation region;

after forming the lightly doped drain/source region, patterning the insulating layer to form a gate spacer on a sidewall of the gate stack; and

forming a source/drain region in the lightly doped drain/source region, the source/drain region having the first doping type.

19. The method of claim 18 , wherein the gate stack is formed above a channel region of the semiconductor fin, and the lightly doped drain/source region is formed beneath the channel region of the semiconductor fin.

20. The method of claim 18 , wherein implanting the dopant in the insulating layer comprises:

depositing a layer of the dopant on the insulating layer during a discharge pulse of a plasma doping process; and

driving the dopant into the insulating layer during an implant pulse of the plasma doping process.