Methods for doping high-k metal gates for tuning threshold voltages

1. A method comprising:

forming a first gate dielectric and a second gate dielectric over a first semiconductor region and a second semiconductor region, respectively;

depositing a lanthanum-containing layer comprising a first portion and a second portion overlapping the first gate dielectric and the second gate dielectric, respectively;

depositing a hard mask comprising a first portion and a second portion overlapping the first portion and the second portion of the lanthanum-containing layer, respectively, wherein the hard mask is free from both of titanium and tantalum;

forming a patterned etching mask to cover the first portion of the hard mask, with the second portion of the hard mask being exposed;

removing the second portion of the hard mask and the second portion of the lanthanum-containing layer; and

performing an anneal to drive lanthanum in the first portion of the lanthanum-containing layer into the first gate dielectric.

2. The method of claim 1 further comprising:

before the anneal, removing the patterned etching mask; and

removing the first portion of the hard mask.

3. The method of claim 1 , wherein the hard mask is a single-layer hard mask.

4. The method of claim 1 further comprising, before the forming the patterned etching mask, performing a plasma treatment on the hard mask.

5. The method of claim 1 , wherein the hard mask is a dual-layer hard mask comprising:

a first sub-layer comprising aluminum nitride, aluminum oxide, or zirconium oxide; and

a second sub-layer over the first sub-layer, wherein the second sub-layer comprises tungsten.

6. The method of claim 1 further comprising forming a non-metal-containing adhesion layer over and contacting the hard mask.

7. The method of claim 1 further comprising:

after the anneal, removing the first portion of the lanthanum-containing layer.

8. The method of claim 7 further comprising:

forming a titanium nitride comprising layer comprising a first portion and a second portion over and contacting the first gate dielectric and the second gate dielectric, respectively.

9. The method of claim 1 further comprising:

before the forming the first gate dielectric and the second gate dielectric, forming a first dummy gate stack between first gate spacers and a second dummy gate stack between second gate spacers; and

removing the first dummy gate stack and the second dummy gate stack to form a first trench between the first gate spacers and a second trench between the second gate spacers, wherein the first gate dielectric and the second gate dielectric are formed to extend into the first trench and the second trench, respectively.

10. The method of claim 1 , wherein the depositing the lanthanum-containing layer comprises depositing a lanthanum oxide layer.

11. A method comprising:

forming a first gate dielectric and a second gate dielectric over a first semiconductor region and a second semiconductor region, respectively;

depositing a lanthanum-containing layer comprising a first portion and a second portion overlapping the first gate dielectric and the second gate dielectric, respectively;

depositing a hard mask comprising a first portion and a second portion overlapping the first portion and the second portion of the lanthanum-containing layer, respectively, wherein the hard mask is free from both of titanium and tantalum;

forming a patterned etching mask to cover the first portion of the hard mask, with the second portion of the hard mask being exposed;

removing the second portion of the hard mask and the second portion of the lanthanum-containing layer;

performing an anneal to drive lanthanum in the first portion of the lanthanum-containing layer into the first gate dielectric; and

after the anneal, removing the first portion of the lanthanum-containing layer.

12. The method of claim 11 further comprising, at a time after the second portion of the hard mask is removed and before the anneal, removing the first portion of the hard mask.

13. The method of claim 11 further comprising, at a time after the anneal and before the first portion of the lanthanum-containing layer is removed, removing the first portion of the hard mask.

14. The method of claim 11 further comprising dispensing a photo resist over and contacting the hard mask, with a contact angle between the photo resist and the hard mask being smaller than about 10 degrees.

15. The method of claim 11 further comprising removing the patterned etching mask before the anneal.

16. The method of claim 11 further comprising removing the first portion of the hard mask before the anneal.

17. The method of claim 11 further comprising forming a work-function layer over each of the first gate dielectric and the second gate dielectric.

18. A method comprising:

forming a first gate dielectric and a second gate dielectric over a first semiconductor region and a second semiconductor region, respectively, wherein both of the first gate dielectric and the second gate dielectric comprise a lanthanum oxide;

depositing a lanthanum-containing layer comprising a first portion and a second portion overlapping and in physical contact with the first gate dielectric and the second gate dielectric, respectively;

depositing a hard mask comprising a first portion and a second portion overlapping the first portion and the second portion of the lanthanum-containing layer, respectively, wherein the hard mask is free from both of titanium and tantalum;

forming a patterned etching mask to cover the first portion of the hard mask, with the second portion of the hard mask being exposed;

removing the second portion of the hard mask and the second portion of the lanthanum-containing layer; and

performing an anneal to drive lanthanum in the first portion of the lanthanum-containing layer into the first gate dielectric.

19. The method of claim 18 , wherein the anneal comprises a spike anneal process performed at a temperature in a range between about 570° C. and about 750° C.

20. The method of claim 18 further comprising, after the anneal, removing the first portion of the lanthanum-containing layer by exposing the first portion of the lanthanum-containing layer to a chemical solution comprising ammonia and hydrogen chloride dissolved therein, wherein the chemical solution is free from hydrogen peroxide therein.