Semiconductor devices and methods of forming the same

1. A method of forming a semiconductor device, the method comprising:

forming a recess in a semiconductor substrate;

forming a gate insulating layer on a bottom portion and an inner wall of the recess;

forming a first metal layer on the gate insulating layer in the recess, the first metal layer including titanium nitride;

forming a second metal layer between opposing sidewalls of a lower portion of the first metal layer in the recess, the second metal layer including tungsten;

forming a metal-containing liner on the first and second metal layers in the recess, the metal-containing liner including lanthanum; and

diffusing metal atoms from the metal-containing liner into an upper portion of the first metal layer in the recess.

2. The method of claim 1 , further comprising:

removing the metal-containing liner, wherein the metal-containing liner is a third metal layer;

forming a fourth metal layer on the second metal layer and on opposing sidewalls of the upper portion of the first metal layer, after removing the metal-containing liner; and

reducing a height of the fourth metal layer and a height of the first metal layer.

3. The method of claim 2 , wherein a top surface of the first metal layer is formed at the same level as a top surface of the fourth metal layer.

4. The method of claim 2 , wherein an interface of the second and fourth metal layers comprises oxide.

5. The method of claim 4 , further comprising removing the oxide from the interface of the second and fourth metal layers.

6. The method of claim 1 , wherein diffusing the metal atoms comprises performing an annealing process on the metal-containing liner.

7. The method of claim 1 , further comprising:

forming a source/drain region in the semiconductor substrate; and

forming a bit line structure on the source/drain region.

8. The method of claim 1 , wherein forming the first metal layer comprises forming a liner in the recess.

9. A method of forming a semiconductor device, the method comprising:

forming a recess in a semiconductor substrate;

forming a first metal layer in the recess;

forming a second metal layer between opposing sidewalls of a lower portion of the first metal layer in the recess;

forming a metal alloy with an upper portion of the first metal layer in the recess, wherein more of the metal alloy is formed with the upper portion of the first metal layer than with the lower portion of the first metal layer;

forming a source/drain region in the semiconductor substrate; and

forming a bit line structure on the source/drain region.

10. The method of claim 9 , wherein forming the source/drain region comprises forming the source/drain region in the semiconductor substrate before forming the recess in the semiconductor substrate.

11. The method of claim 9 , wherein forming the source/drain region comprises forming the source/drain region in the semiconductor substrate after forming the metal alloy with the upper portion of the first metal layer in the recess.

12. The method of claim 9 , wherein forming the metal alloy comprises implanting metal ions into the upper portion of the first metal layer in the recess.

13. The method of claim 9 , wherein forming the metal alloy comprises:

forming a third metal layer on the first and second metal layers in the recess; and

diffusing metal atoms from the third metal layer into the upper portion of the first metal layer in the recess.

14. The method of claim 13 , further comprising:

removing the third metal layer; and

forming a fourth metal layer on the second metal layer and on opposing sidewalls of the upper portion of the first metal layer, after removing the third metal layer.

15. The method of claim 9 , wherein:

forming the first metal layer comprises forming a titanium nitride liner in the recess;

the lower and upper portions of the first metal layer comprise lower and upper portions, respectively, of the titanium nitride liner;

forming the metal alloy comprises implanting or diffusing lanthanum atoms into the upper portion of the titanium nitride liner;

a vertical thickness, in the recess, of the upper portion of the titanium nitride liner is between 200 Angstroms and 300 Angstroms; and

a concentration of lanthanum atoms in the lower portion of the titanium nitride liner is less than 0.01 percent.

16. A method of forming a semiconductor device, the method comprising:

forming a recess in a semiconductor substrate;

forming a first metal layer in the recess;

forming a second metal layer between opposing sidewalls of a lower portion of the first metal layer in the recess, wherein the lower portion of the first metal layer comprises a first work function control portion;

forming a second work function control portion by forming a metal alloy with an upper portion of the first metal layer in the recess, wherein forming the metal alloy comprises implanting metal ions or diffusing metal atoms into the upper portion of the first metal layer in the recess, and wherein more of the metal alloy is in the second work function control portion than in the first work function control portion;

forming a source/drain region in the semiconductor substrate; and

forming a bit line structure on the source/drain region.

17. The method of claim 16 , wherein forming the metal alloy comprises implanting the metal ions into the upper portion of the first metal layer in the recess.

18. The method of claim 16 , wherein forming the metal alloy comprises:

forming a third metal layer in the recess; and

diffusing the metal atoms from the third metal layer into the upper portion of the first metal layer in the recess.