Work function tuning in semiconductor devices
The present disclosure describes a method for forming a semiconductor device having a work function metal layer doped with tantalum to mitigate oxygen diffusion and improve device threshold voltage. The method includes forming a gate dielectric layer on a channel structure and forming a work function metal layer on the gate dielectric layer. The gate dielectric layer includes an interfacial layer on the channel structure and a high-k dielectric layer on the interfacial layer. The method further includes doping the work function metal layer and the gate dielectric layer with tantalum.
1. A method, comprising:
forming a gate dielectric layer on a channel structure, wherein the gate dielectric layer comprises an interfacial layer on the channel structure and a high-k dielectric layer on the interfacial layer;
forming a work function metal layer on the gate dielectric layer; and
diffusing tantalum into the work function metal layer and the gate dielectric layer.
2. The method of claim 1 , wherein doping the work function metal layer and the gate dielectric layer comprises soaking the work function metal layer with a tantalum precursor for about 0.5 second to about 1800 seconds.
3. The method of claim 1 , wherein doping the work function metal layer and the gate dielectric layer comprises forming a tantalum nitride layer on a titanium nitride layer.
4. The method of claim 3 , wherein a ratio of a thickness of the tantalum nitride layer to a thickness of the titanium nitride layer ranges from about 0.1 to about 1.5.
5. The method of claim 1 , further comprising:
forming an additional work function metal layer on the work function metal layer; and
doping the additional work function metal layer with the tantalum.
6. The method of claim 1 , further comprising:
forming a glue layer on the work function metal layer; and
forming a metal fill on the glue layer.
7. The method of claim 1 , wherein doping the work function metal layer and the gate dielectric layer comprises performing the doping at a temperature from about 150° C. to about 550° C.
8. The method of claim 1 , wherein doping the work function metal layer and the gate dielectric layer comprises performing the doping under a pressure from about 0.1 torr to about 50 torr.
9. The method of claim 1 , wherein the work function metal layer is a p-type work function metal comprising titanium nitride, tungsten nitride, tungsten carbon nitride, or titanium silicon nitride.
10. A method, comprising:
forming a gate dielectric layer on a channel structure, wherein the gate dielectric layer comprises an interfacial layer on the channel structure and a high-k dielectric layer on the interfacial layer;
depositing a work function metal layer on the gate dielectric layer with a titanium precursor, a nitrogen precursor, and a tantalum precursor;
diffusing tantalum in the work function metal layer into the gate dielectric layer; and
forming a metal fill on the work function metal layer.
11. The method of claim 10 , wherein depositing the work function metal layer comprises:
delivering the titanium precursor for a first pulse time; and
delivering the tantalum precursor for a second pulse time different from the first pulse time.
12. The method of claim 11 , wherein a ratio of the first pulse time to the second pulse time ranges from about 0.15 to about 10.
13. The method of claim 10 , wherein depositing the work function metal layer comprises performing the deposition at a temperature from about 150° C. to about 550° C.
14. The method of claim 10 , wherein depositing the work function metal layer comprises performing the deposition under a pressure from about 0.1 torr to about 50 torr.
15. A method, comprising:
forming a gate dielectric layer in a gate stack opening, wherein the gate dielectric layer comprises an interfacial layer and a high-k dielectric layer;
forming a work function metal layer on the gate dielectric layer;
diffusing tantalum into the work function metal layer and the gate dielectric layer under a thermal condition; and
depositing a metal fill in the gate stack opening and on the work function layer.
16. The method of claim 15 , wherein forming the work function metal layer comprises soaking the work function metal layer and the high-k dielectric layer with a tantalum precursor for about 0.5 second to about 1800 seconds.
17. The method of claim 16 , wherein the work function metal layer and the high-k dielectric layer are soaked at a temperature from about 150° C. to about 550° C.
18. The method of claim 16 , wherein the work function metal layer and the high-k dielectric layer are soaked under a pressure from about 0.1 torr to about 50 torr.
19. The method of claim 15 , wherein forming the work function metal layer comprises:
forming a titanium nitride layer on the high-k dielectric layer; and
forming a tantalum nitride layer on the titanium nitride layer.
20. The method of claim 19 , wherein a ratio of a thickness of the tantalum nitride layer to a thickness of the titanium nitride layer ranges from about 0.1 to about 1.5.