Sidewall image transfer structures

1. A method for forming a semiconductor device, the method comprising:

forming a layer of sacrificial gate material on an initial oxide layer on an active region;

forming a first sacrificial mandrel on the layer of sacrificial gate material and forming a second sacrificial mandrel on the layer of sacrificial gate material, where the first sacrificial mandrel is formed from a first sacrificial material and the second sacrificial mandrel is formed from a second sacrificial material;

forming a first oxide layer on the first sacrificial mandrel and a second oxide layer on the second sacrificial mandrel, the first oxide layer having a thickness that is less than the second oxide layer;

removing the first sacrificial mandrel and the second sacrificial mandrel to define a first spacer and a second spacer, the first spacer having a width that is less than a width of the second spacer;

removing exposed portions of the layer of sacrificial gate material to expose the initial oxide layer on the active region and form a first sacrificial gate and a second sacrificial gate over channel regions of the active region;

forming a spacer adjacent to the first sacrificial gate and a spacer adjacent to the second sacrificial gate;

depositing an insulator layer over a source/drain region;

removing the first sacrificial gate and the second sacrificial gate to form a first cavity and a second cavity that expose channel regions of the active region; and

forming a first gate stack in the first cavity and a second gate stack in the second cavity.

2. The method of claim 1 , further comprising forming a hardmask on the layer of sacrificial gate material prior to forming first sacrificial mandrel on the layer of sacrificial gate material.

3. The method of claim 1 , wherein the first sacrificial material includes Si and the second sacrificial material includes SiGe.

4. The method of claim 1 , wherein the first sacrificial material is dissimilar from the second sacrificial material.

5. The method of claim 1 , wherein the first sacrificial material has a slower oxidation rate than the second sacrificial material.

6. The method of claim 1 , wherein the first sacrificial mandrel and the second sacrificial mandrel are formed by:

forming a hardmask on the layer of sacrificial gate material;

forming a layer of the first sacrificial material on the hardmask;

removing a portion of the first sacrificial material to expose a portion of the hardmask;

depositing the second sacrificial material on the exposed portions of the hardmask; and

patterning and removing portions of the first sacrificial material and the second sacrificial material to expose portions of the hardmask and form the first sacrificial mandrel and the second sacrificial mandrel.

7. The method of claim 1 , wherein the layer of sacrificial gate material includes amorphous silicon.

8. The method of claim 1 , wherein the second gate stack has a greater length than the second gate stack.

9. A method for forming a semiconductor device, the method comprising:

forming a semiconductor fin;

forming a layer of sacrificial gate material on an initial oxide layer on the semiconductor fin;

forming a first sacrificial mandrel on the layer of sacrificial gate material and forming a second sacrificial mandrel on the layer of sacrificial gate material, where the first sacrificial mandrel is formed from a first sacrificial material and the second sacrificial mandrel is formed from a second sacrificial material;

forming a first oxide layer on the first sacrificial mandrel and a second oxide layer on the second sacrificial mandrel, the first oxide layer having a thickness that is less than the second oxide layer;

removing the first sacrificial mandrel and the second sacrificial mandrel to define a first spacer and a second spacer, the first spacer having a width that is less than a width of the second spacer;

removing exposed portions of the layer of sacrificial gate material to expose the initial oxide layer on the semiconductor fin and form a first sacrificial gate and a second sacrificial gate over channel regions of the semiconductor fin;

forming a spacer adjacent to the first sacrificial gate and a spacer adjacent to the second sacrificial gate;

depositing an insulator layer over a source/drain region;

removing the first sacrificial gate and the second sacrificial gate to form a first cavity and a second cavity that expose channel regions of the semiconductor fin; and

forming a first gate stack in the first cavity and a second gate stack in the second cavity.

10. The method of claim 9 , further comprising forming a hardmask on the layer of sacrificial gate material prior to forming first sacrificial mandrel on the layer of sacrificial gate material.

11. The method of claim 9 , wherein the first sacrificial material is dissimilar from the second sacrificial material.

12. The method of claim 9 , wherein the first sacrificial mandrel and the second sacrificial mandrel are formed by:

forming a hardmask on the layer of sacrificial gate material;

forming a layer of the first sacrificial material on the hardmask;

removing a portion of the first sacrificial material to expose a portion of the hardmask;

depositing the second sacrificial material on the exposed portions of the hardmask; and

patterning and removing portions of the first sacrificial material and the second sacrificial material to expose portions of the hardmask and form the first sacrificial mandrel and the second sacrificial mandrel.

13. The method of claim 9 , wherein the layer of sacrificial gate material includes amorphous silicon.

14. The method of claim 9 , wherein the second gate stack has a greater length than the second gate stack.

15. The method of claim 9 , wherein the semiconductor fin is arranged on an insulator layer.

16. The method of claim 9 , wherein the spacer adjacent to the first sacrificial gate includes a nitride material.