Directly forming SiGe fins on oxide

1. A method of forming a semiconductor structure, said method comprising:

providing a structure comprising a plurality of semiconductor mandrel structures containing a nitride-containing hard mask cap and extending upward from a semiconductor substrate, wherein a first oxide isolation structure is located between each semiconductor mandrel structure and on exposed portions of said semiconductor substrate;

forming a silicon germanium alloy fin on opposing sidewalls of each semiconductor mandrel structure in a pFET device region of said semiconductor substrate, wherein each silicon germanium alloy fin has a bottommost surface that directly contacts a topmost surface of one of said first oxide isolation structures;

removing each nitride-containing hard mask cap and each semiconductor mandrel structure adjoining each silicon germanium alloy fin; and

forming a second oxide isolation structure between each first oxide isolation structure, said second oxide isolation structure having a topmost surface coplanar with a topmost surface of each first oxide isolation structure and a bottommost surface that is deeper than a bottommost surface of each first oxide isolation structure.

2. The method of claim 1 , further comprising forming a functional gate structure straddling each silicon germanium alloy fin.

3. The method of claim 1 , wherein one sidewall surface of each silicon germanium alloy fin is vertically aligned to a sidewall edge of one of said first oxide isolation structures.

4. The method of claim 1 , wherein prior to forming said silicon germanium alloy fins, a block mask is formed over each semiconductor mandrel structure within an nFET device region of said semiconductor substrate.

5. The method of claim 4 , further comprising:

removing said block mask over each semiconductor mandrel structure within said nFET device region;

forming another block mask over said silicon germanium alloy fins and said semiconductor mandrel structures in said pFET device region;

forming n-channel semiconductor material fins from opposing sidewalls of each semiconductor mandrel structure and directly on a topmost surface of one of said first oxide isolation structure in said nFET device region; and

removing said another bock mask.

6. The method of claim 5 , where said removing each semiconductor mandrel structure adjoining each silicon germanium alloy fin, further removes each semiconductor mandrel structure adjoining each n-channel semiconductor material fin.

7. The method of claim 6 , further comprising forming a functional gate structure straddling each n-channel semiconductor material fin.

8. The method of claim 1 , wherein said forming said silicon germanium alloy fin comprises an epitaxial growth process.

9. The method of claim 1 , wherein said removing each semiconductor mandrel structure adjoining each silicon germanium alloy fin comprises:

forming a nitride-containing liner surrounding each silicon germanium alloy fin and atop each nitride-containing hard mask cap;

forming a first oxide structure having a topmost surface that is coplanar with a topmost surface so said nitride-containing liner that is located atop each nitride-containing hard mask cap;

removing a portion of said nitride-containing liner located above each semiconductor mandrel structure;

removing each nitride-containing hard mask cap; and

performing an anisotropic etch to remove each semiconductor mandrel structure.

10. The method of claim 9 , wherein said anisotropic etch forms a recessed region in said semiconductor substrate, and wherein a lower portion of said second oxide isolation structure is present in said recessed region.