Bulk nanosheet with dielectric isolation

1. A method of forming a nanosheet device structure with dielectric isolation, the method comprising the steps of:

forming a plurality of nanosheets as a stack on a bulk semiconductor wafer;

patterning the nanosheets to form one or more nanowire stacks and one or more trenches between the nanowire stacks;

forming spacers covering sidewalls of the nanowire stacks; and

oxidizing a top portion of the bulk semiconductor wafer through the trenches, wherein the oxidizing step forms a dielectric isolation region in the top portion of the bulk semiconductor wafer,

wherein the method further comprises the step of: implanting at least one dopant into the top portion of the bulk semiconductor wafer prior to performing the step of forming the nanosheets on the bulk semiconductor wafer, wherein the at least one dopant is configured to increase an oxidation rate of the top portion of the bulk semiconductor wafer.

2. The method of claim 1 , wherein the at least one dopant is selected from the group consisting of: fluorine, phosphorous, and combinations thereof.

3. The method of claim 1 , wherein the at least one dopant is implanted into the top portion of the bulk semiconductor wafer at a dose of from about 5×10 15 atoms/cm 2 to about 5×10 16 atoms/cm 2 , and ranges therebetween.

4. The method of claim 1 , wherein the bulk semiconductor wafer has a thickness of from about 0.1 millimeters to about 0.75 millimeters, and ranges therebetween.

5. The method of claim 1 , wherein the top portion of the bulk semiconductor wafer comprises a first thickness of from about 100 angstroms to about 500 angstroms, and ranges therebetween, of the bulk semiconductor wafer.

6. The method of claim 1 , wherein the plurality of nanosheets comprises alternating layers of a sacrificial material and a channel material as the stack on the bulk semiconductor wafer.

7. The method of claim 6 , wherein the sacrificial material comprises silicon germanium (SiGe) and the channel material comprises silicon (Si).

8. The method of claim 1 , wherein a first nanosheet in the stack present on the bulk semiconductor wafer is thicker than other nanosheets in the stack.

9. The method of claim 8 , wherein the first nanosheet in the stack has a thickness of from about 20 nanometers to about 35 nanometers, and ranges therebetween.

10. The method of claim 8 , wherein the other nanosheets in the stack have a thickness of from about 10 nanometers to about 25 nanometers, and ranges therebetween.

11. The method of claim 1 , further comprising the step of:

filling the trenches with a trench oxide prior to oxidizing the top portion of the bulk semiconductor wafer.

12. The method of claim 1 , wherein the oxidizing step comprises the step of:

annealing the bulk semiconductor wafer in an oxygen ambient under conditions sufficient to form the dielectric isolation region in the top portion of the bulk semiconductor wafer.

13. The method of claim 12 , wherein the conditions comprise annealing the bulk semiconductor wafer at a temperature of from about 750° C. to about 1,500° C., and ranges therebetween.

14. The method of claim 12 , wherein the conditions comprise annealing the bulk semiconductor wafer for a duration of from about 60 seconds to about 1 hour, and ranges therebetween.

15. A method of forming a nanowire field effect transistor (FET) device, the method comprising the steps of:

implanting at least one dopant into a top portion of a bulk semiconductor wafer, wherein the at least one dopant is configured to increase an oxidation rate of the top portion of the bulk semiconductor wafer, and wherein the at least one dopant is selected from the group consisting of: fluorine, phosphorous, and combinations thereof;

forming a plurality of nanosheets as a stack on the bulk semiconductor wafer, wherein the plurality of nanosheets comprises alternating layers of a sacrificial material and a channel material as the stack on the bulk semiconductor wafer;

patterning the nanosheets to form one or more nanowire stacks and one or more trenches between the nanowire stacks;

forming spacers covering sidewalls of the nanowire stacks;

oxidizing the top portion of the bulk semiconductor wafer through the trenches, wherein the oxidizing step forms a dielectric isolation region in the top portion of the bulk semiconductor wafer;

removing the spacers;

selectively removing portions of the layers of the sacrificial material from the nanowire stacks in a channel region of the FET device releasing portions of the channel material from the nanowire stacks, wherein the portions of the channel material released from the nanowire stacks form nanowire channels of the FET device; and

forming a gate surrounding the nanowire channels in the channel region of the device.

16. The method of claim 15 , further comprising the step of:

filling the trenches with a trench oxide prior to oxidizing the top portion of the bulk semiconductor wafer.

17. The method of claim 15 , further comprising the steps of:

forming at least one dummy gate over the nanowire stacks in the channel region of the FET device;

forming dummy gate spacers on opposite sides of the dummy gate;

forming doped source and drain regions of the FET device;

burying the dummy gate in a gap fill dielectric material;

removing the dummy gate forming at least one gate trench in the gap fill dielectric; and

forming the gate in the gate trench.