Semiconductor patterning and resulting structures

1. A method comprising:

depositing a hard mask over a target layer, wherein depositing the hard mask comprises:

depositing a first hard mask layer having a first density, the first hard mask layer being a first oxide layer; and

depositing a second hard mask layer over the first hard mask layer, the second hard mask layer having a second density greater than the first density, and the second hard mask layer being a second oxide layer;

forming a plurality of mandrels over the hard mask;

depositing a spacer layer over and along sidewalls of the plurality of mandrels;

patterning the spacer layer to provide a plurality of spacers on the sidewalls of the plurality of mandrels;

after patterning the spacer layer, removing the plurality of mandrels;

transferring a pattern the plurality of spacers to the hard mask; and

patterning the target layer using the hard mask as a mask.

2. The method of claim 1 , wherein the first hard mask layer and the second hard mask layer each comprises silicon oxide.

3. The method of claim 1 , wherein the first hard mask layer comprises silicon oxide, and wherein the second hard mask layer comprises silicon oxynitride, silicon oxycarbon nitride, or a combination thereof.

4. The method of claim 1 , wherein depositing the second hard mask layer comprises depositing the second hard mask layer and the first hard mask layer in-situ.

5. The method of claim 1 , wherein depositing the first hard mask layer comprises a chemical vapor deposition (CVD) process, and wherein depositing the second hard mask layer comprises an atomic layer deposition (ALD) process that is performed ex-situ of the CVD process.

6. The method of claim 1 , wherein the first hard mask layer has a first thickness, wherein the second hard mask layer has a second thickness, and wherein a ratio of the second thickness to the first thickness is in a range of 1:6 to 1:4.

7. The method of claim 6 , wherein the second thickness is in a range of about 50 Å to about 150 Å, and wherein the first thickness is in a range of about 400 Å to about 1000 Å.

8. The method of claim 6 , wherein the target layer is a semiconductor substrate, and wherein patterning the target layer using the hard mask comprises patterning semiconductor fins in the semiconductor substrate.

9. A method comprising:

depositing a first oxide hard mask layer over a target layer;

depositing a second oxide hard mask layer over the first oxide hard mask layer, wherein the second oxide hard mask layer has a greater density than the first oxide hard mask layer, and wherein a density of the second oxide hard mask layer is at least 1.8 g/cm 3 ;

depositing a mandrel layer over the second oxide hard mask layer;

etching the mandrel layer to define a plurality of mandrels;

forming spacers on sidewalls of the plurality of mandrels;

removing the plurality of mandrels to define openings between the spacers;

using the spacers as a mask to pattern the first oxide hard mask layer; and

using the first oxide hard mask layer as a mask to pattern the target layer.

10. The method of claim 9 , wherein removing the plurality of mandrels etches a recess into the second oxide hard mask layer.

11. The method of claim 10 , wherein a depth of the recess is less than 3 nm.

12. The method of claim 9 , wherein using the spacers as the mask to pattern the first oxide hard mask layer comprises consuming the spacers and the second oxide hard mask layer while etching the first oxide hard mask layer.

13. The method of claim 9 , wherein using the first oxide hard mask layer as the mask to pattern the target layer comprises removing upper portions of the first oxide hard mask layer.

14. The method of claim 9 , wherein depositing the second oxide hard mask layer comprises depositing the second oxide hard mask layer in a same process chamber as depositing the first oxide hard mask layer.

15. The method of claim 14 , wherein depositing the second oxide hard mask layer comprises depositing the second oxide hard mask layer in a different process chamber as depositing the first oxide hard mask layer.

16. A method comprising:

depositing a first oxide layer over a semiconductor layer;

depositing a second oxide layer over the first oxide layer, wherein the second oxide layer has a greater density than the first oxide layer, and wherein the second oxide layer is thinner than the first oxide layer;

forming a plurality of mandrels over the second oxide layer;

forming spacers on sidewalls of the plurality of mandrels;

removing the plurality of mandrels to define openings between the spacers, wherein removing the plurality of mandrels etches recesses in the second oxide layer;

using the spacers as a mask to pattern the first oxide layer; and

using the first oxide layer as a mask to pattern the semiconductor layer.

17. The method of claim 16 , wherein a ratio of a thickness of the second oxide layer to a thickness of the first oxide layer is in a range of 1:6 to 1:4.

18. The method of claim 16 , wherein a respective depth of each of the recesses is less than 3 nm.

19. The method of claim 16 , wherein the second oxide layer comprises silicon oxide, silicon oxynitride, silicon oxycarbon nitride, or a combination thereof.

20. The method of claim 16 , wherein the second oxide layer completely covers the first oxide layer while removing the plurality of mandrels.