Method for forming interconnect structure

1. A method comprising:

depositing a first dielectric layer over a first conductive feature;

depositing a first mask layer over the first dielectric layer, the first mask layer comprising tungsten carbide;

depositing a second mask layer over the first mask layer, the second mask layer comprising titanium nitride;

patterning a first opening in the first mask layer and the second mask layer, the first opening having a first width;

patterning a second opening in a bottom surface of the first opening, the second opening extending into the first dielectric layer, the second opening having a second width, the second width being less than the first width; and

extending the first opening into the first dielectric layer and extending the second opening through the first dielectric layer to expose a top surface of the first conductive feature.

2. The method of claim 1 , wherein the first mask layer has a first thickness in a range of 30 Å to 200 Å.

3. The method of claim 1 , wherein the second mask layer has a second thickness in a range of 20 Å to 100 Å.

4. The method of claim 1 , further comprising filling the first opening and the second opening with a conductive material.

5. The method of claim 4 , wherein filling the first opening forms a conductive line in the first opening, the conductive line having a third width in a range of 5 nm to 40 nm.

6. The method of claim 4 , wherein filling the second opening forms a conductive via in the second opening, the conductive via having a fourth width in a range of 5 nm to 30 nm.

7. The method of claim 1 , further comprising forming a third mask layer over the second mask layer.

8. The method of claim 7 , wherein the third mask layer comprises silicon oxide.

9. A method comprising:

depositing a first mask layer over a low-k dielectric layer, the first mask layer being silicon oxide;

depositing a second mask layer over the first mask layer, the second mask layer being tungsten carbide;

depositing a third mask layer over the second mask layer, the third mask layer being titanium nitride;

depositing a fourth mask layer over the third mask layer, the fourth mask layer being silicon oxide;

patterning the second mask layer, the third mask layer, and the fourth mask layer to form a trench;

extending the trench into the low-k dielectric layer by etching through the first mask layer;

forming a conductive line by filling the trench with a conductive material; and

removing the first mask layer, the second mask layer, the third mask layer, and the fourth mask layer.

10. The method of claim 9 , wherein etching through the first mask layer comprises etching the first mask layer with a fluorine-based etchant.

11. The method of claim 9 , wherein the second mask layer has a Young's modulus in a range of 500 MPa to 2000 MPa.

12. The method of claim 9 , wherein removing the fourth mask layer is performed while etching through the first mask layer.

13. The method of claim 9 , wherein forming the conductive line comprises planarizing the conductive material, and wherein the first mask layer, the second mask layer, and the third mask layer are removed by the planarizing of the conductive material.

14. A method comprising:

forming a first mask layer over a first dielectric layer, the first dielectric layer being over a first conductive feature, the first mask layer comprising tungsten carbide;

forming a second mask layer over the first mask layer, the second mask layer comprising titanium nitride;

patterning the first mask layer and the second mask layer; and

after patterning the first mask layer and the second mask layer, forming an opening extending into the first dielectric layer by etching the first dielectric layer with a fluorine-based etchant using the first mask layer and the second mask layer as an etching mask, the opening exposing a top surface of the first conductive feature, the etching the first dielectric layer with the fluorine-based etchant being performed at a first temperature, wherein a first byproduct of the fluorine-based etchant with the first mask layer has a boiling point less than the first temperature.

15. The method of claim 14 , wherein a second byproduct of the fluorine-based etchant with the second mask layer has a boiling point greater than the first temperature.

16. The method of claim 15 , wherein the second byproduct is TiF 4 .

17. The method of claim 14 , wherein the first byproduct is WF 6 .

18. The method of claim 14 , wherein the etching the first dielectric layer is performed with a plasma etching process, and the fluorine-based etchant is CF 4 .

19. The method of claim 18 , wherein the plasma etching process is performed at a temperature in a range of 20° C. to 60° C.

20. The method of claim 14 , wherein the first temperature is room temperature.