Forming method of interconnect structure

1 . A method of forming an interconnect structure, comprising:

forming a multilayer stack on a substrate comprising a wiring layer, wherein the multilayer stack comprises:

an extreme low-k dielectric layer above the wiring layer; and

a mask layer above the extreme low-k dielectric layer;

etching the multilayer stack to form a trench, wherein the trench exposes the extreme low-k dielectric layer;

forming a spacer on a sidewall of the trench, wherein the spacer physically contacts the mask layer;

etching the extreme low-k dielectric layer to form a via hole, wherein the via hole exposes the wiring layer;

filling the trench and the via hole with a conductive material; and

performing a planarization process on the multilayer stack to remove the spacer.

2 . The method of claim 1 , wherein a tensile stress of the spacer is between 1 GPa and 1.7 GPa after forming the spacer on the sidewall of the trench.

3 . The method of claim 1 , wherein the spacer covers an entire sidewall of the mask layer in the trench after forming the spacer on the sidewall of the trench.

4 . The method of claim 1 , wherein the spacer physically contacts the extreme low-k dielectric layer after forming the spacer on the sidewall of the trench.

5 . The method of claim 1 , wherein the spacer extends from the mask layer to a bottom surface of the trench after forming the spacer on the sidewall of the trench.

6 . The method of claim 1 , wherein the mask layer has a first thickness in a first direction vertical to a top surface of the extreme low-k dielectric layer, the spacer has a second thickness in a second direction parallel to the top surface of the extreme low-k dielectric layer, and the first thickness is larger than the second thickness.

7 . The method of claim 1 , wherein the mask layer and the spacer comprises a same nitride material.

8 . The method of claim 1 , wherein the mask layer comprises a first nitride material, the spacer comprises a second nitride material or a carbon nitride material different from the first nitride material.

9 . The method of claim 1 , wherein the multilayer stack further comprises:

a dielectric layer between the extreme low-k dielectric layer and the mask layer, wherein a hardness of the dielectric layer is higher than that of the extreme low-k dielectric layer.

10 . The method of claim 9 , wherein the step of etching the multilayer stack to form the trench further comprises etching the dielectric layer, and wherein the spacer physically contacts the dielectric layer after forming the spacer on the sidewall of the trench.

11 . The method of claim 1 , wherein the multilayer stack further comprises:

an adhesion layer between the mask layer and the extreme low-k dielectric layer, wherein the step of etching the multilayer stack to form the trench comprises etching the adhesion layer, and wherein the spacer physically contacts the adhesion layer after forming the spacer on the sidewall of the trench.

12 . The method of claim 1 , wherein after etching the multilayer stack to form the trench, a first distance between a bottom surface of the trench and a top surface of the extreme low-k dielectric layer is smaller than a second distance between the bottom surface of the trench and a bottom surface of the extreme low-k dielectric layer.

13 . A method of forming an interconnect structure, comprising:

forming an extreme low-k dielectric layer above a substrate comprising a wiring layer;

performing a first deposition process to form a first titanium nitride layer above the extreme low-k dielectric layer;

performing a first etching process to form a first trench in the first titanium nitride layer and the extreme low-k dielectric layer;

performing a second deposition process to form a second titanium nitride layer on a sidewall of the first trench;

performing a second etching process to form a via hole in the extreme low-k dielectric layer, wherein the via hole exposes the wiring layer;

filling the first trench and the via hole with a conductive material; and

removing the first titanium nitride layer and the second titanium nitride layer.

14 . The method of claim 13 , wherein a first growing direction of the first deposition process is different from a second growing direction of the second deposition process.

15 . The method of claim 13 , wherein a first bias applied during the first deposition process is different from a second bias applied during the second deposition process.

16 . The method of claim 13 , wherein after performing the second deposition process, the first titanium nitride layer has a first thickness in a first direction vertical to a top surface of the extreme low-k dielectric layer, the second titanium nitride layer has a second thickness in a second direction parallel to the top surface of the extreme low-k dielectric layer, and a ratio of the first thickness over the second thickness is between 1.5 and 2.5.

17 . The method of claim 13 , wherein a tensile stress of the second titanium nitride layer is larger than or equal to 1 GPa after performing the second deposition process.

18 . The method of claim 13 , wherein a bottom surface of the second titanium nitride layer is lower than a bottom surface of the first titanium nitride layer after performing the second deposition process.

19 . The method of claim 13 , wherein the second titanium nitride layer extends from the first titanium nitride layer to a position lower than a top surface of the extreme low-k dielectric layer after performing the second deposition process.

20 . The method of claim 13 , wherein the step of performing the second etching process further comprises etching the extreme low-k dielectric layer along a sidewall of the second titanium nitride layer to form a second trench, and wherein the step of filling the first trench and the via hole with the conductive material comprises filling the second trench with the conductive material.