Structure and method for FinFET device

1. A method for fabricating a fin-type field-effect transistor (FinFET) device, the method comprising:

forming a first fin structure over a substrate;

forming a dielectric layer over the first fin structure;

forming a trench within the dielectric layer, wherein the first fin structure is exposed in a bottom of the trench;

depositing a first semiconductor material layer within the trench;

depositing a second semiconductor material layer over the first semiconductor material layer within the trench;

recessing the dielectric layer to laterally expose the first semiconductor material layer; and

etching the exposed first semiconductor material layer to reveal the second semiconductor material layer, wherein at least a portion of the first semiconductor material layer underneath the second semiconductor material layer remains intact.

2. The method of claim 1 , wherein forming the trench in the dielectric layer includes:

performing a chemical mechanical polishing (CMP) to remove excessive dielectric layer and expose a top surface of the first fin structure;

recessing the first fin structure to leave a first trench in the dielectric layer; and

enlarging the first trench to form the trench with a vertical sidewall profile.

3. The method of claim 2 , wherein the first semiconductor material along the sidewalls of the trench carries the vertical sidewall profile of the trench.

4. The method of claim 3 , wherein the second semiconductor material layer deposited over the first semiconductor material layer carries the vertical sidewall profile.

5. The method of claim 1 , wherein the second semiconductor material layer is deposited by epitaxially growing from a bottom of the remaining trench.

6. The method of claim 1 , wherein the dielectric layer is recessed to make its top surface below the first semiconductor material layer at the bottom of the trench.

7. The method of claim 6 , wherein outer portions of the first semiconductor material layer at the bottom of the trench is removed during etching exposed first semiconductor material layer.

8. The method of claim 1 , wherein the dielectric layer is recessed to make its top surface above the first semiconductor material layer at the bottom of the trench.

9. The method of claim 8 , further comprising:

removing the first semiconductor material layer above the dielectric layer;

recessing the dielectric layer further to expose the remaining first semiconductor material layer; and

trimming an outer layer of the exposed remaining first semiconductor material layer.

10. The method of claim 1 , further comprising:

forming a high-k/metal gate over the substrate, including wrapping over the second semiconductor material layer and the remaining first semiconductor material layer.

11. A method for fabricating a fin-type field-effect transistor (FinFET) device, the method comprising:

forming a first fin structure, surrounding by a dielectric layer, over a substrate;

recessing the first fin structure to form a trench in the dielectric layer;

enlarging the trench to have a vertical sidewall profile;

depositing conformably a first semiconductor material layer over sidewalls and bottom of the trench;

epitaxially growing a second semiconductor material from bottom of the remaining trench;

recessing the dielectric layer to laterally expose the first semiconductor material layer;

removing the exposed first semiconductor material layer along the sidewall of the second semiconductor material layer, but does not substantially etch the second semiconductor material layer, wherein at least a portion of the first semiconductor material layer underneath the second semiconductor material layer remains intact; and

forming a high-k/metal gate over the substrate, including wrapping over the second semiconductor material layer and the remaining first semiconductor material layer underneath the second semiconductor material layer.

12. The method of claim 11 , wherein the first semiconductor material along the sidewalls of the trench carries the vertical sidewall profile of the trench.

13. The method of claim 12 , wherein the second semiconductor material layer deposited over the first semiconductor material layer carries a vertical sidewall profile.

14. The method of claim 11 , wherein the dielectric layer is recessed to make its top surface below the first semiconductor material layer at the bottom of the trench.

15. The method of claim 14 , wherein outer portions of the first semiconductor material layer at the bottom of the trench is removed during etching exposed first semiconductor material layer.

16. The method of claim 11 , wherein the dielectric layer is recessed to make its top surface above the first semiconductor material layer at the bottom of the trench.

17. The method of claim 16 , further comprising:

removing the first semiconductor material layer above the dielectric layer;

recessing the dielectric layer further to expose the remaining first semiconductor material layer; and

trimming an outer layer of the exposed remaining first semiconductor material layer.