Composite work function layer formation using same work function material

1. A method comprising:

forming a gate dielectric layer on a semiconductor region;

depositing a first aluminum-containing work function layer using a first aluminum-containing precursor, wherein the first aluminum-containing work function layer is over the gate dielectric layer, wherein the first aluminum-containing work function layer is deposited at a first temperature;

depositing a second aluminum-containing work function layer using a second aluminum-containing precursor different from the first aluminum-containing precursor, wherein the second aluminum-containing work function layer is deposited over the first aluminum-containing work function layer, wherein the second aluminum-containing work function layer is deposited at a second temperature different from the first temperature; and

forming a conductive region over the second aluminum-containing work function layer.

2. The method of claim 1 , wherein both of the first aluminum-containing work function layer and the second aluminum-containing work function layer comprise TiAlC.

3. The method of claim 2 , wherein the first aluminum-containing work function layer is deposited to have a higher aluminum atomic percentage than the second aluminum-containing work function layer.

4. The method of claim 1 , wherein the first aluminum-containing precursor comprises triethylaluminum (TEA), and the second aluminum-containing precursor comprises Trimethylaluminum (TMA).

5. The method of claim 1 , wherein the first aluminum-containing work function layer is performed using a first atomic layer deposition (ALD) process for a first number of cycles, and wherein the second aluminum-containing work function layer is performed using a second ALD process for a second number of cycles different from the first number of cycles.

6. The method of claim 1 , wherein the first aluminum-containing precursor comprises tritertbutylaluminum (TTBA), and the second aluminum-containing precursor comprises Trimethylaluminum (TMA).

7. The method of claim 1 , wherein both of the first aluminum-containing work function layer and the second aluminum-containing work function layer are deposited using chemical vapor deposition.

8. The method of claim 7 , wherein the first aluminum-containing work function layer has a first per-cycle-thickness greater than a second per-cycle-thickness of the second aluminum-containing work function layer.

9. The method of claim 1 , wherein the first aluminum-containing work function layer and the second aluminum-containing work function layer are in-situ deposited without vacuum break in between.

10. A method comprising:

forming a gate dielectric over a semiconductor region; depositing a work function layer over the gate dielectric, wherein the work function layer comprises TiAlC, and wherein the work function layer comprises:

depositing a first sub-layer having a first aluminum atomic percentage, wherein the first sub-layer is deposited at a first temperature; and

depositing a second sub-layer over the first sub-layer, wherein the second sub-layer has a second aluminum atomic percentage lower than the first aluminum atomic percentage, wherein the second sub-layer is deposited at a second temperature different from the first temperature; and

depositing a glue layer over and physically contacting the work function layer.

11. The method of claim 10 , wherein a ratio of the second aluminum atomic percentage to the first aluminum atomic percentage is smaller than about 90 percent.

12. The method of claim 10 , wherein the first sub-layer is deposited using a first aluminum-containing precursor, and the second sub-layer is deposited using a second aluminum-containing precursor different from the first aluminum-containing precursor.

13. The method of claim 12 , wherein the first aluminum-containing precursor comprises triethylaluminum (TEA), and the second aluminum-containing precursor comprises tritertbutylaluminum (TTBA) or Trimethylaluminum (TMA).

14. The method of claim 12 , wherein the first aluminum-containing precursor comprises tritertbutylaluminum (TTBA), and the second aluminum-containing precursor comprises Trimethylaluminum (TMA).

15. The method of claim 10 , wherein the first temperature is higher than the second temperature.

16. The method of claim 10 , wherein the depositing the glue layer comprises depositing a titanium nitride layer.

17. A method comprising:

depositing a semiconductor fin;

depositing a high-k gate dielectric on the semiconductor fin; and

forming a gate electrode over the high-k gate dielectric and comprising:

depositing a work function layer comprising aluminum, the depositing the work function layer comprising:

depositing a lower part, wherein a peak aluminum atomic percentage of the work function layer is in the lower part of the work function layer, and wherein the lower part is deposited at a first temperature; and

depositing an upper part over the lower part, wherein atomic percentages in the upper part are lower than aluminum atomic percentages in the lower part, and wherein the upper part is deposited at a second temperature different from the first temperature; and

depositing a glue layer over and contacting the work function layer.

18. The method of claim 17 , wherein the lower part and the upper part are deposited using different precursors.

19. The method of claim 17 , wherein both of the depositing the lower part and the depositing the upper part comprise depositing TiAlC layers.

20. The method of claim 17 , wherein the depositing the lower part and the depositing the upper part are performed using different precursors selected from triethylaluminum (TEA), tritertbutylaluminum (TTBA), and Trimethylaluminum (TMA).