Method for forming interconnect structure

1. A method for forming an interconnect structure, the method comprising:

forming a first dielectric layer on a substrate;

forming a conductive via in the first dielectric layer;

forming a first metal layer, a second metal layer, and a third metal layer sequentially over the first dielectric layer, wherein the first metal layer has a bottom surface that is in contact with the conductive via and the entire bottom surface of the first metal layer is flat;

etching the third metal layer to form a metal pillar;

forming a cap layer over the metal pillar and the second metal layer, wherein the cap layer comprises Ta, TaN, TiN, Co, Ru, Zr, graphene, or combinations thereof;

etching the cap layer and the second metal layer; and

after etching the cap layer and the second metal layer, etching the first metal layer to form a metal line under the etched second metal layer.

2. The method of claim 1 , wherein a material of the first metal layer is different from a material of the second metal layer, the material of the second metal layer is different from a material of the third metal layer, and etching the third metal layer comprises:

performing a first lithography operation to form a first photoresist on the third metal layer; and

performing a first etch operation to expose the second metal layer.

3. The method of claim 2 , wherein forming the cap layer is such:

that the cap layer lines a top surface of the second metal layer, sidewalls of the metal pillar, and a top surface of the metal pillar.

4. The method of claim 3 , wherein etching the cap layer and the second metal layer comprises:

performing a second lithography operation to form a second photoresist on the cap layer and a third photoresist on the second photoresist, wherein the third photoresist is patterned to cover the metal pillar;

performing a second etch operation to expose the first metal layer and to form an intermediate metal layer beneath the metal pillar; and

removing the second photoresist and the third photoresist.

5. The method of claim 4 , further comprising:

forming an etch stop layer between the first dielectric layer and the first metal layer; and

after etching the first metal layer, forming a second dielectric layer over the cap layer.

6. The method of claim 1 , wherein a thickness of the first metal layer is in a range substantially from 20 angstroms to 700 angstroms, and a thickness of the second metal layer is in a range substantially from 5 angstroms to 200 angstroms, and a thickness of the third metal layer is in a range substantially from 50 angstroms to 1000 angstroms.

7. A method for forming an interconnect structure, the method comprising:

forming a first dielectric layer on a substrate;

forming an opening in the first dielectric layer;

depositing a first metal layer over the first dielectric layer;

depositing a metal conductive layer over and in contact with the first metal layer;

depositing a second metal layer over the metal conductive layer;

etching the second metal layer to form a metal pillar; and

forming a cap layer over and in contact with a top surface of the metal pillar and the metal conductive layer.

8. The method of claim 7 , wherein a material of the first metal layer is different from a material of the metal conductive layer, the material of the metal conductive layer is different from a material of the second metal layer, and etching the second metal layer comprises:

performing a first lithography operation to form a first photoresist on the second metal layer; and

performing a first etch operation to expose the metal conductive layer and to form the metal pillar.

9. The method of claim 8 , wherein the material of the first metal layer and the second metal layer comprises aluminum, copper, cobalt, tungsten, ruthenium, or zirconium, wherein the material of the metal conductive layer comprises tantalum, tantalum nitride, titanium nitride, copper, cobalt, tungsten, ruthenium, or graphene.

10. The method of claim 8 , wherein forming the cap layer is such:

that the cap layer lines a top surface of the metal conductive layer, sidewalls of the metal pillar, and the top surface of the metal pillar, wherein a material of the cap layer comprises tantalum, tantalum nitride, titanium nitride, copper, cobalt, ruthenium, or graphene.

11. The method of claim 10 , further comprising:

forming an etch stop layer between the first dielectric layer and the first metal layer;

performing a second lithography operation to form a second photoresist on the cap layer and a third photoresist on the second photoresist, wherein the third photoresist is patterned to cover the metal pillar;

performing a second etch operation to etch the cap layer and the metal conductive layer, so as to expose the first metal layer and to form an intermediate metal layer beneath the metal pillar;

removing the second photoresist and the third photoresist;

performing a third etch operation to etch the first metal layer, so as to expose the etch stop layer and to form a metal line beneath the intermediate metal layer; and

forming a second dielectric layer over the cap layer.

12. The method of claim 7 , wherein a thickness of the first metal layer is in a range substantially from 20 angstroms to 700 angstroms, and a thickness of the metal conductive layer is in a range substantially from 5 angstroms to 200 angstroms, and a thickness of the second metal layer is in a range substantially from 50 angstroms to 1000 angstroms.

13. A method for forming an interconnect structure, the method comprising:

providing a substrate;

sequentially depositing a first metal layer, a second metal layer, and a third metal layer over the substrate;

etching the third metal layer;

forming a cap layer that simultaneously lines a top surface and a sidewall of the third metal layer;

forming a first photoresist over the cap layer;

forming a second photoresist over the first photoresist;

patterning the second photoresist;

etching, using the patterned second photoresist as an etching mask, the cap layer, and the second metal layer;

removing the first and second photoresists;

after removing the first and second photoresists, etching the first metal layer to form a metal line; and

after etching the first metal layer, depositing a dielectric layer that surrounds the metal line.

14. The method of claim 13 , further comprising:

etching the second metal layer to form an intermediate metal layer; and

after etching the second metal layer, depositing the dielectric layer that surrounds the intermediate metal layer.

15. The method of claim 13 , further comprising:

etching the third metal layer to form a metal pillar; and

after etching the third metal layer, depositing the dielectric layer that surrounds metal pillar.

16. The method of claim 15 , wherein etching the first metal layer is after etching the third metal layer.

17. The method of claim 15 , further comprising:

forming the cap layer over the metal pillar; and

etching the first metal layer using the cap layer as a mask.

18. The method of claim 17 , wherein depositing the dielectric layer is after forming the cap layer.

19. The method of claim 1 , wherein forming the second metal layer is such that the second metal layer is in contact with the first metal layer.

20. The method of claim 1 , wherein forming the third metal layer is such that the second metal layer is in contact with the third metal layer.