Apparatus and method for FinFETs

1. A method comprising:

forming a first isolation region in a substrate;

forming a second isolation region in the substrate;

forming a recess between the first isolation region and the second isolation region by removing a portion of the substrate;

performing a surface treatment on the recess to form a cloak-shaped recess, wherein the cloak-shaped recess extends into the first isolation region and the second isolation region; and

forming a cloak-shaped active region through an epitaxial growth.

2. The method of claim 1 further comprising:

forming a first drain/source region and a second drain/source region in the cloak-shaped active region suing an ion implantation process, with a channel connected between the first drain/source region and the second drain/source region.

3. The method of claim 1 further comprising:

applying a chemical mechanical polishing process on the cloak-shaped active region to form a planar surface;

removing upper portions of the first isolation region and the second isolation region;

depositing a gate dielectric layer on a top surface of the cloak-shaped active region; and

forming a gate electrode over the gate dielectric layer.

4. The method of claim 3 , wherein the gate dielectric is further formed on sidewalls of a top portion of the cloak-shaped active region.

5. The method of claim 1 , wherein the forming the cloak-shaped active region comprises forming a silicon germanium epitaxial region in the cloak-shaped recess.

6. The method of claim 1 further comprising:

applying an etching process to form a trench in the substrate; and

filling a dielectric material in the trench to form the first isolation region.

7. A method comprising:

forming isolation regions extending into a semiconductor substrate;

removing a portion of the semiconductor substrate to form a recess, wherein the portion of the semiconductor substrate is between opposite sidewalls of the isolation regions, with the recess comprising a V-shaped bottom surface;

after the removing the portion of the semiconductor substrate, performing a treatment to extend the V-shaped bottom surface into the isolation regions; and

epitaxially growing a semiconductor material in the recess.

8. The method of claim 7 , wherein in the treatment, a lower portion of the recess is expanded more into the isolation regions than a respective upper portion of the recess.

9. The method of claim 7 , wherein the treatment comprises a plasma treatment using an oxygen-containing gas and a fluorine-containing gas.

10. The method of claim 7 , wherein the V-shaped bottom surface comprises:

a first bottom surface joining a first sidewall surface of the recess to form a first angle; and

a second bottom surface joining a second sidewall surface of the recess to form a second angle, wherein after the treatment, the first angle and the second angle are between about 100 degrees and about 110 degrees.

11. The method of claim 7 further comprising:

after the epitaxially growing the semiconductor material, performing a Chemical Mechanical Polish (CMP) to level a top surface of the semiconductor material with top surfaces of the isolation regions;

recessing the isolation regions, wherein a top portion of the semiconductor material is over top surfaces of remaining portions of the isolation regions to form a fin;

forming a gate dielectric on a top surface and sidewalls of the fin; and

forming a gate electrode over the gate dielectric.

12. The method of claim 7 , wherein the removing the portion of the semiconductor substrate is performed using a wet etch, and wherein the treatment is performed using a dry etch.

13. The method of claim 7 , wherein the epitaxially growing the semiconductor material in the recess comprises growing silicon germanium.

14. A method comprising:

forming isolation regions extending into a semiconductor substrate;

performing a wet etch to remove a portion of the semiconductor substrate, wherein the portion of the semiconductor substrate is between opposite sidewalls of the isolation regions to form a recess;

after the wet etch, performing a dry etch to expand the recess into the isolation regions, wherein a lower portion of the recess is expanded more into the isolation region than a respective upper portion of the recess; and

epitaxially growing a semiconductor material in the recess.

15. The method of claim 14 , wherein the wet etch forms the recess comprising a V-shaped bottom surface, and wherein the dry etch expands the V-shaped bottom surface into the isolation regions.

16. The method of claim 15 , wherein the V-shaped bottom surface comprises:

a first bottom surface joining a first sidewall surface of the recess to form a first angle; and

a second bottom surface joining a second sidewall surface of the recess to form a second angle, wherein after the dry etch, the first angle and the second angle are between about 100 degrees and about 110 degrees.

17. The method of claim 14 , wherein the dry etch is performed using an oxygen-containing gas and a fluorine-containing gas as process gases.

18. The method of claim 14 further comprising:

after epitaxially growing the semiconductor material, performing a Chemical Mechanical Polish (CMP) to level a top surface of the semiconductor material with top surfaces of the isolation regions;

recessing the isolation regions, wherein a top portion of the semiconductor material is over top surfaces of remaining portions of the isolation regions to form a fin;

forming a gate dielectric on a top surface and sidewall of the fin; and

forming a gate electrode over the gate dielectric.

19. The method of claim 14 , wherein the wet etch is stopped before a bottom of the recess reaches a level as deep as bottom surfaces of the isolation regions.

20. The method of claim 14 , wherein the semiconductor material in the recess comprises silicon germanium.