Method of fabricating semiconductor fins by enhancing oxidation of sacrificial mandrels sidewalls through angled ion beam exposure

1. A method of fabricating semiconductor fins on a substrate, comprising:

patterning a film stack to produce two or more sacrificial mandrels having first and second sidewalls on opposing sides of each of the mandrels and a capping layer on a top surface of each of the two or more sacrificial mandrels;

exposing each of the first sidewalls of the two or more sacrificial mandrels to an ion beam at a first angle to the surface of the substrate to make the exposed first sidewalls of each of the two or more sacrificial mandrels more susceptible to oxidation, wherein the capping layer covers the top surface of each of the two or more sacrificial mandrels during the exposure to the ion beam;

oxidizing the first and second sidewalls of each of the two or more sacrificial mandrels to form a plurality of oxide pillars on opposing sides of each of the mandrels;

removing the two or more sacrificial mandrels; and

forming spacers on opposite sides of each of the plurality of oxide pillars to produce a spacer pattern.

2. The method of claim 1 , wherein the two or more sacrificial mandrels comprise amorphous silicon.

3. The method of claim 1 , wherein the ion beam impinges the sidewall on one side of each of the two or more sacrificial mandrels at an angle that shadows the opposite sidewall of each of the two or more sacrificial mandrels, wherein the capping layer on the top surface of each of the two or more sacrificial mandrels shadows at least a portion of each of the underlying sacrificial mandrels from the ion beam.

4. The method of claim 1 , wherein the oxide pillars formed by oxidizing the first sidewalls of each of the two or more sacrificial mandrels have different widths than the oxide pillars formed by oxidizing the second sidewalls of each of the two or more sacrificial mandrels.

5. The method of claim 4 , which further comprises removing the plurality of oxide pillars; and

transferring the spacer pattern to the substrate to produce a plurality of fins, wherein the plurality of fins have a predefined pitch.

6. The method of claim 5 , which further comprises forming trenches having varying depths between the plurality of fins.

7. The method of claim 1 , wherein the spacer formation comprises conformal deposition on at least opposite sides of each of the plurality of oxide pillars.

8. The method of claim 7 , wherein the spacers comprise amorphous carbon.

9. The method of claim 1 , wherein the first sidewall of the two or more sacrificial mandrels is exposed to an ion beam comprising a p-type dopant.

10. The method of claim 9 , wherein the p-type dopant comprises boron and the sacrificial mandrels comprise amorphous silicon.