Methods for forming fins

1. A method for forming a set of fins from a substrate, the method comprising:

providing a stack over the substrate, the stack including a first oxide over the substrate, a first nitride over the first oxide, a second oxide over the first nitride, and a first hardmask over the second oxide

patterning the first hardmask to form a first set of hardmask fins over the second oxide;

oxidizing the first set of hardmask fins to convert the first set of hardmask fins into a set of oxide fins;

using the set of oxide fins as a mask, etching the second oxide and the first nitride to expose portions of the first oxide thereunder such that remaining portions of the second oxide and the first nitride remain disposed beneath the set of oxide fins thereby defining a set of mask stacks; and

using the set of mask stacks as a mask, etching the exposed portions of the first oxide and the substrate thereby forming the set of fins from the substrate.

2. The method of claim 1 , wherein the stack further includes a second hardmask over the first hardmask and a mandrel pattern over the second hardmask, wherein the patterning of the first hardmask includes:

transferring the mandrel pattern into the first and second hardmask to expose portions of the second oxide thereunder;

removing the mandrel pattern thereby defining a second set of hardmask fins over remaining portions of the second oxide, the second set of hardmask fins including remaining portions of the second hardmask over the first hardmask;

removing any hardmask fin from the second set of hardmask fins not defined by the first set of hardmask fins; and

removing the second hardmask from over the first hardmask in each hardmask fin of the second set of hardmask fins thereby defining the first set of hardmask fins.

3. The method of claim 1 , wherein the stack further includes a second hardmask over the first hardmask and a mandrel pattern over the second hardmask, wherein the patterning of the first hardmask includes:

transferring the mandrel pattern into the first and second hardmask to expose the second oxide thereunder;

removing the mandrel pattern thereby defining the first set of hardmask fins over remaining portions of the second oxide, the first set of hardmask fins including remaining portions of the second hardmask over the first hardmask; and

removing at least one hardmask fin from the first set of hardmask fins.

4. The method of claim 3 , wherein the oxidizing of the first set of hardmask fins includes oxidizing the first hardmask without oxidizing the second hardmask of each hardmask fin such that the second hardmask is disposed over each oxide fin in the set of oxide fins.

5. The method of claim 4 , further comprising:

removing the second hardmask from over each oxide fin in the set of oxide fins.

6. The method of claim 5 , wherein the first hardmask includes polysilicon and the second hardmask includes silicon nitride.

7. The method of claim 1 , further comprising:

forming spacers on opposing sidewalls of each mask stack in the set of mask stacks, wherein the etching of the exposed portions of the first oxide and the substrate to form the set of fins from the substrate includes using each mask stack together with the spacers as a mask.

8. The method of claim 1 , wherein a width of each hardmask fin in the first set of hardmask fins is approximately equal to 6 nanometers.

9. The method of claim 1 , wherein a width of each oxide fin in the set of oxide fins includes a critical dimension of about two times the width of each hardmask fin in the first set of hardmask fins.

10. The method of claim 1 , wherein the oxidizing the first set of hardmask fins includes performing a furnace steam oxidation or a rapid thermal process oxidation.