Semiconductor devices including a gate structure in a substrate

1. A semiconductor device comprising:

a semiconductor substrate;

a source/drain region in the semiconductor substrate; and

a gate structure in a recess in the semiconductor substrate, the gate structure comprising a liner comprising:

a first portion; and

a second portion on the first portion, wherein the second portion:

is closer, than the first portion, to the source/drain region; and

comprises a metal alloy, wherein:

the second portion of the liner is smaller than the first portion of the liner;

the gate structure comprises a plurality of implanted and/or diffused atoms; and

a majority of the plurality of implanted and/or diffused atoms are in the metal alloy of the second portion of the liner.

2. The semiconductor device of claim 1 , further comprising:

a gate electrode in the recess, wherein the liner is on opposing sidewalls of the gate electrode; and

a bit line on the source/drain region, wherein the source/drain region comprises a non-elevated source/drain region.

3. The semiconductor device of claim 1 ,

wherein a vertical thickness, in the recess, of the second portion of the liner is between 2 Angstroms and 300 Angstroms, and

the plurality of implanted and/or diffused atoms in the metal alloy comprises lanthanum (La), strontium (Sr), antimony (Sb), yttrium (Y), aluminum (Al), tantalum (Ta), hafnium (Hf), or iridium (Ir) atoms.

4. The semiconductor device of claim 3 , wherein the vertical thickness of the second portion of the liner is between 200 Angstroms and 300 Angstroms.

5. The semiconductor device of claim 4 , wherein the gate structure further comprises a gate electrode that is between opposing sidewalls of the second portion of the liner and that protrudes beyond an uppermost surface of the second portion of the liner.

6. The semiconductor device of claim 1 , wherein:

the metal alloy of the second portion of the liner comprises titanium nitride and lanthanum oxide; and

the first portion of the liner comprises titanium nitride.

7. The semiconductor device of claim 6 , wherein the gate structure further comprises a layer of tungsten that extends between opposing sidewalls of the first portion of the liner comprising the titanium nitride and between opposing sidewalls of the second portion of the liner comprising the metal alloy.

8. The semiconductor device of claim 1 , wherein:

the first and second portions of the liner comprise first and second work function control portions, respectively;

the second work function control portion comprises the metal alloy; and

the metal alloy of the second work function control portion comprises a smaller work function than the first work function control portion.

9. The semiconductor device of claim 8 , wherein the gate structure further comprises a gate electrode:

adjacent the second work function control portion; and

comprising a lower resistivity than polysilicon.

10. The semiconductor device of claim 9 , wherein the gate electrode comprises a first thickness that is thicker than a second thickness of the second work function control portion, such that the gate electrode protrudes beyond an uppermost surface of the second work function control portion.

11. The semiconductor device of claim 9 , wherein:

the gate electrode comprises a first metal layer; and

the gate structure further comprises a second metal layer adjacent the first work function control portion.

12. The semiconductor device of claim 11 , wherein:

the first and second metal layers comprise tungsten;

the first and second work function control portions comprise titanium nitride; and

the plurality of implanted and/or diffused atoms comprises lanthanum atoms.

13. The semiconductor device of claim 1 , wherein:

the source/drain region comprises a first source/drain region;

the semiconductor device further comprises a second source/drain region;

the second portion of the liner comprises a sidewall comprising a portion that extends between the first and second source/drain regions; and

the first and second source/drain regions are on respective sides of the recess.

14. A semiconductor device comprising:

a substrate;

first and second source/drain regions in the substrate; and

a buried gate structure in the substrate, the buried gate structure comprising:

a first work function control portion; and

a second work function control portion on the first work function control portion, wherein the second work function control portion:

is closer, than the first work function control portion, to the first and second source/drain regions; and

comprises a metal alloy comprising a greater, relative to the first work function control portion, concentration of implanted and/or diffused metal atoms.

15. The semiconductor device of claim 14 , wherein the implanted and/or diffused metal atoms comprise atoms of a metal that comprises a smaller work function than titanium (Ti), titanium nitride (TiN), titanium aluminum nitride (TiAlN), titanium aluminum carbide (TiAlC), titanium aluminum carbonitride (TiAlCN), titanium silicon carbonitride (TiSiCN), tantalum (Ta), tantalum nitride (TaN), tantalum aluminum nitride (TaAlN), tantalum aluminum carbonitride (TaAlCN), or tantalum silicon carbonitride (TaSiCN).

16. The semiconductor device of claim 14 ,

wherein the buried gate structure further comprises a gate electrode that is between opposing sidewalls of the second work function control portion, and

wherein the metal alloy of the second work function control portion comprises titanium nitride and lanthanum oxide.

17. A semiconductor device comprising:

a substrate;

a source/drain region in the substrate;

a bit line on the source/drain region; and

a buried gate structure in the substrate, the buried gate structure comprising:

a liner comprising first and second portions, wherein the second portion:

is closer, than the first portion, to the source/drain region; and

comprises a metal oxide comprising a first concentration of implanted and/or diffused metal atoms that is greater than a second concentration of the implanted and/or diffused metal atoms in the first portion; and

a gate electrode that is adjacent a sidewall of the second portion of the liner and that comprises a lower resistivity than polysilicon.

18. The semiconductor device of claim 17 ,

wherein the second portion of the liner extends adjacent a portion of a sidewall of the source/drain region, and

wherein the gate electrode protrudes upwardly beyond an uppermost surface of the second portion of the liner.

19. The semiconductor device of claim 17 ,

wherein the implanted and/or diffused metal atoms comprise lanthanum atoms, and

wherein the second concentration of the implanted and/or diffused metal atoms in the first portion of the liner is less than 0.01 percent.

20. The semiconductor device of claim 17 , wherein the implanted and/or diffused metal atoms comprise lanthanum (La), strontium (Sr), antimony (Sb), yttrium (Y), aluminum (Al), tantalum (Ta), hafnium (Hf), or iridium (Ir) atoms.