Multi-layer structure having a dense middle layer

1. A method of fabricating a semiconductor structure, the method comprising:

depositing a hard mask over a substrate;

depositing a multi-layer structure over the hard mask, the multi-layer structure comprising a bottom layer, a first middle layer over the bottom layer, a second middle layer over the first middle layer, a top layer over the second middle layer, wherein the first middle layer comprises a SiC x H y O z material, the SiC x H y O z material having a silicon-to-silicon bond content in a range from about 0.5% to about 5%; and

patterning the multi-layer structure to form a patterned first middle layer having openings; and

etching the hard mask through the openings in the patterned first middle layer.

2. The method of claim 1 , wherein the first middle layer is deposited by a plasma enhanced chemical vapor deposition process at a process temperature in a range from about 50° C. to about 350° C. and in a process pressure in a range from about 0.5 torr to about 20 torr.

3. The method of claim 1 , wherein the first middle layer is deposited by a chemical vapor deposition process, the chemical vapor deposition process comprising flowing a silicon precursor, a carbon precursor, and an oxygen precursor.

4. The method of claim 3 , wherein the silicon precursor is selected from a group consisting of silane (SiH 4 ), disilane (Si 2 H 4 ), trisilane (Si 2 H 4 ), and a combination thereof.

5. The method of claim 3 , wherein the carbon precursor is selected from the group consisting of tetraethyl orthosilicate (TEOS), dimethyldiethoxysilane (mDEOS), methane (CH 4 ), ethane (C 2 H 6 ), propane (C 3 H 8 ), α-Terpinene, trimethylsilane (C 3 H 10 Si), tetramethylsilane (C 4 H 12 Si), benzene (C 6 H 6 ), and a combination thereof.

6. The method of claim 1 , wherein the first middle layer is deposited by an atomic layer deposition process, the atomic layer deposition process comprises flowing a silicon-carbon precursor in a first pulse and flowing an oxygen precursor in a second pulse.

7. The method of claim 6 , wherein the silicon-carbon precursor comprises bis-diethylamino-silane (SiH 2 [N(C 2 H 5 ) 2 ] 2 ).

8. The method of claim 6 , wherein the atomic layer deposition process comprises a plasma-enhanced atomic layer deposition process.

9. A method of fabricating a semiconductor structure, the method comprising:

forming a multi-layer structure over a hard mask layer, the multi-layer structure comprising a bottom layer, a first middle layer over the bottom layer, a second middle layer over the first middle layer, a top layer over the second middle layer, wherein the top layer comprises a photoresist material, wherein the first middle layer and the second middle layer comprise silicon-containing materials, wherein the second middle layer has a lower silicon-to-silicon bond content than the first middle layer;

patterning the top layer with a photolithography process to form openings;

etching the first middle layer to form a patterned first middle layer having openings forming sidewall taper angles in a range from about 70° to about 90°; and

etching the hard mask layer through the openings in the patterned first middle layer.

10. The method of claim 9 , wherein the patterned top layer comprises a Si—O—Si backbone.

11. The method of claim 9 , the first middle layer comprises a SiCxHyOz material deposited by plasma enhanced CVD or plasma-assisted ALD.

12. The method of claim 11 , wherein the top layer is deposited by a spin-on process.

13. The method of claim 12 , wherein the bottom layer is deposited by a spin-on process.

14. The method of claim 13 , wherein the top layer and the bottom layer comprise a C x H y O z material.

15. A method of fabricating a semiconductor structure, the method comprising:

forming a multi-layer hard mask comprising an intermetal layer and a silicon-containing layer over the intermetal layer;

forming a multi-layer structure over the multi-layer hard mask, the multi-layer structure comprising a bottom layer, a first middle layer having a thickness in a range from about 50 Å to about 300 Å over the bottom layer, and a top photoresist layer over the first middle layer;

patterning the top photoresist layer with a photolithography process to form a patterned top photoresist layer;

performing a descum process over the patterned top photoresist layer;

etching the first middle layer through the patterned top photoresist layer to form a patterned first middle layer having openings to the bottom layer, wherein the first middle layer comprises a material with an etch selectivity of five or more in comparison to the bottom layer during the etching of the first middle layer;

etching the bottom layer through the openings in the patterned first middle layer to form a patterned bottom layer having openings to the silicon-containing layer;

etching the silicon-containing layer through the openings in the first middle layer and through the openings in the bottom layer to form a patterned silicon-containing layer having openings to the intermetal layer; and

etching the intermetal layer through openings in the patterned silicon-containing layer to form a patterned intermetal layer.

16. The method of claim 15 , wherein after the etching the bottom layer, at least a portion of the patterned first middle layer remains.

17. The method of claim 15 , further comprising etching a dielectric layer through the openings of the patterned intermetal layer to form a patterned dielectric layer having openings.

18. The method of claim 17 , wherein the openings of the patterned dielectric layer are to conductive features.

19. The method of claim 17 , further comprising depositing a metal fill in the openings in the patterned dielectric layer.

20. The method of claim 19 , wherein the metal fill has a pitch in a range of about 40 nm or less.