Dense finFET SRAM

1. A method for fabricating a semiconductor device, comprising:

applying an angled ion implantation to at least one of a first and second structure such that one of the first and second structures has a greater oxidation rate than an other of the first and second structures, wherein a first oxide having a first thickness forms on said first structure and a second oxide of a second thickness forms on said second structure;

forming a first spacer on the first oxide and a second spacer on the second oxide, wherein the first and second spacer provide an etch mask; and

patterning a layer below the first spacer and the second spacer using the etch mask to form at least a first plurality of fin structures having a first pitch and a second plurality of fin structures having a second pitch.

2. The method of claim 1 , wherein the first plurality of fin structures provides a first device including merged fins and a second plurality of fin structures provides a second device including unmerged fins.

3. The method of claim 2 , wherein the first device and the second device form an SRAM cell.

4. The method of claim 2 , wherein the first device includes at least one of a pull down device and a pass gate device.

5. The method of claim 2 , wherein the second device includes a pull up device.

6. The method of claim 2 , wherein the merged fins include merged sources and/or drains.

7. The method of claim 1 , wherein the first pitch is equal to 20 nm and the second pitch is equal to 30 nm.

8. The method of claim 1 , wherein the first structure and the second structure are patterned from a semiconductor substrate.

9. The method of claim 1 , wherein the applying of said angled ion implantation to said at least one of said first and second structure comprises applying said angled ion implantation to the second structure such that the first structure is protected and a second angled ion implantation to the first structure such that the second structure is protected, wherein exposed portions of the first and second structures have an altered rate of oxidation.

10. The method of claim 9 further comprising performing oxidation to form thicker or thinner oxide portions on the exposed portions of the first and second structures relative to unexposed portions of the first and second structures.

11. The method of claim 10 further comprising:

removing oxide portions to an underlying layer of the first and second structures;

removing the first and second structures;

forming the first and second spacer about a periphery of remaining oxide portions; and

removing the remaining oxide portions.

12. The method as recited in claim 11 , wherein applying the first angled ion implantation to the second structure such that the first structure is protected and the second angled ion implantation to the first structure such that the second structure is protected includes selecting an angle of attack, direction of ion implantation and type of ions to be implanted to selectively modify the oxidation rate of exposed portions of the first and second structures.

13. The method as recited in claim 11 , wherein applying the first angled ion implantation to the second structure such that the first structure is protected includes forming a first mask over the first structure and wherein applying the second angled ion implantation to the first structure such that the second structure is protected includes forming a second mask over the second structure.

14. The method as recited in claim 11 , wherein applying the first angled ion implantation to the second structure such that the first structure is protected includes implanting the second structure with at least one of ions to enhance a rate of oxidation and ions to reduce a rate of oxidation.

15. The method as recited in claim 11 , wherein the ions to enhance the rate of oxidation includes fluorine ions.

16. The method as recited in claim 14 , wherein the ions to reduce the rate of oxidation includes nitrogen ions.

17. The method as recited in claim 11 , wherein applying the second angled ion implantation to the first structure such that the second structure is protected includes implanting the first structure with at least one of fluorine to enhance a rate of oxidation and nitrogen to reduce a rate of oxidation.

18. The method as recited in claim 11 , wherein applying the first angled ion implantation to the second structure such that the first structure is protected includes implanting the second structure with ions to enhance a rate of oxidation and applying the second angled ion implantation to the first structure such that the second structure is protected includes implanting the first structure with ions to reduce a rate of oxidation.

19. A method for fabricating a semiconductor device, comprising:

applying an angled ion implantation to at least one of a first and second structure such that one of the first and second structures has a greater oxidation rate than an other of the first and second structures, wherein a first oxide having a first thickness forms on said first structure and a second oxide of a second thickness forms on said second structure;

forming a first spacer on the first oxide and a second spacer on the second oxide, wherein the first and second spacer provide an etch mask;

patterning a layer below the first spacer and the second spacer using the etch mask to form at least a first plurality of fin structures having a first pitch and a second plurality of fin structures having a second pitch; and

forming a first device including merged fins on the first plurality of fin structures and a second device including unmerged fins on the second plurality of fin structures.

20. The method of claim 19 , wherein the first device and the second device form an SRAM cell, wherein the first device includes at least one of a pull down device and a pass gate device and the second device includes a pull up device.