FinFET device with gate oxide layer

1. A semiconductor device, the device comprising:

a substrate;

one or more fins each including a first semiconductor layer formed over the substrate;

an oxide layer formed wrapping over an upper portion of each of the one or more fins; and

a gate stack including a high-K (HK) dielectric layer and a metal gate (MG) electrode formed wrapping over the oxide layer,

wherein the first semiconductor layer includes silicon germanium (SiGex), and

wherein the oxide layer includes silicon germanium oxide (SiGexOy).

2. The device of claim 1 , wherein the upper portion of each of the one or more fins includes the first semiconductor layer, and

wherein the oxide layer is formed wrapping over the first semiconductor layer.

3. The device of claim 2 , wherein each of the one or more fins includes one or more protruding portions including germanium (Ge) migrated from the SiGex in the first semiconductor layer towards the substrate along sides of the fins, and

wherein a depth of each of the one or more protruding portions is in a range from about 2.2 nm to about 4.8 nm.

4. The device of claim 1 , wherein each of the one or more fins further includes a second semiconductor layer including silicon (Si) formed over the first semiconductor layer, and

wherein the upper portion of the each of the one or more fins includes the second semiconductor layer.

5. The device of claim 4 , wherein each of the one or more fins includes one or more protruding portions including germanium (Ge) migrated from the SiGex in the first semiconductor layer towards the Si in the second semiconductor layer along sides of the fins, and

wherein a depth of each of the one or more protruding portions is in a range from about 2.2 nm to about 4.8 nm.

6. The device of claim 1 , wherein a Ge concentration x of SiGex is in a range from about 10% to about 100%.

7. The device of claim 1 , wherein a Ge concentration at a center of a fin is at least about 10% greater than a Ge concentration at a surface of the fin.

8. The device of claim 1 , wherein a Ge concentration x of SiGexOy has a graded change in the oxide layer.

9. The device of claim 1 , wherein a diffusion depth of Ge from each of the one or more fins to a corresponding oxide layer is in a range from about 2 nm to about 3 nm.

10. The device of claim 1 , wherein a thickness of the oxide layer is in a range from about 0.5 nm to about 4 nm.

11. The device of claim 1 , further comprising:

isolation regions formed over the substrate to separate the fins;

source and drain features formed over the substrate and separated by the gate stack; and

interlayer dielectric layers formed over the source/drain features and separated by the gate stack.

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

providing a device precursor, the device precursor including:

a substrate; and

one or more fins each including one or more semiconductor layers formed over the substrate;

forming a gate trench in a dielectric layer formed over the substrate and between the one or more fins;

depositing an oxide layer to wrap over an upper portion of each of the one or more fins exposed in the gate trench;

performing a plasma treatment to the deposited oxide layer; and

forming a gate stack including a high-K (HK) dielectric layer and a metal gate (MG) electrode to fill in the gate trench.

13. The method of claim 12 , wherein the depositing the oxide layer includes using a plasma enhanced atomic layer deposition process in a temperature range from about 150° C. to about 400° C.

14. The method of claim 13 , wherein the plasma enhanced atomic layer deposition process includes using an oxygen (O2) plasma with a power range from about 10 W to about 30 W, and

wherein the power used in the plasma enhanced atomic layer deposition is less than a power used in the plasma treatment.

15. The method of claim 12 , wherein the performing the plasma treatment includes using an oxygen (O2) plasma with a flow rate in a range from about 10 sccm to about 1000 sccm.

16. The method of claim 12 , wherein the performing the plasma treatment includes using an oxygen (O2) plasma with a power range from about 200 W to about 600 W.

17. The method of claim 12 , wherein the performing the plasma treatment includes applying the O2 plasma in a time range from about 10 seconds to about 150 seconds and in a temperature range from about 150° C. to about 400° C.

18. The method of claim 12 , wherein the depositing the oxide layer and the performing the plasma treatment are performed in-situ in a same deposition tool.

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

epitaxially growing a silicon germanium (SiGe) layer over a silicon (Si) substrate;

etching the SiGe layer and the Si substrate to form one or more fins and one or more isolation trenches;

forming one or more isolation features in the one or more isolation trenches;

forming a gate trench in a dielectric layer formed over the substrate;

depositing an oxide layer to wrap over an upper portion of each of the one or more fins exposed in the gate trench;

performing an oxygen (O2) plasma treatment to the deposited oxide layer; and

forming a gate stack including a high-K (HK) dielectric layer and a metal gate (MG) electrode to fill in the gate trench,

wherein the oxide layer includes a silicon germanium oxide (SiGexOy) layer.

20. The method of claim 19 , wherein the depositing the oxide layer includes using a low temperature deposition performed in a temperature range from about 150° C. to about 350° C.