Interconnect with composite layers and method for fabricating the same

1. An interconnect structure, comprising:

a semiconductor substrate with a first conductor thereon;

a dielectric layer overlying the semiconductor substrate having an opening therein exposing the first conductor, wherein the width of the opening is from 100 to 800 Å;

a composite diffusion barrier layer formed by atomic layer deposition lining the sidewalls of the opening, wherein the composite diffusion barrier layer comprises a first layer of titanium nitride or tantalum nitride, either of which is treated with plasma in hydrogen ambient, and a second layer of titanium nitride or tantalum nitride on the treated first layer; and

a second conductor filling the opening and electrically connecting the underlying first conductor.

2. The interconnect structure as claimed in claim 1 , wherein the first conductor is composed of a material selected from group consisting of copper, copper alloy, aluminum, aluminum alloy, titanium, tantalum, tungsten, metal silicide, metal alloy and metal compound.

3. The interconnect structure as claimed in claim 1 , wherein the dielectric layer comprises a silicon oxide-containing material.

4. The interconnect structure as claimed in claim 1 , wherein the dielectric constant (k) of the dielectric layer is less than 2.8.

5. The interconnect structure as claimed in claim 1 , wherein the thickness of the composite diffusion barrier layer is from 30 to 300 Å.

6. The interconnect structure as claimed in claim 1 , wherein the composite diffusion barrier layer is composed of dual titanium nitride layers or dual tantalum nitride layers.

7. The interconnect structure as claimed in claim 1 , wherein the second conductor is composed of a material selected from the group consisting of copper, copper alloy, aluminum and aluminum alloy.

8. The interconnect structure as claimed in claim 1 , further comprising a low-resistivity metal layer having a thickness from 10 to 100 Å lining the bottom and the sidewalls of the opening.

9. The interconnect structure as claimed in claim 8 , wherein the low-resistivity metal layer is composed of a material selected from the group consisting of titanium and tantalum.

10. An interconnect structure, comprising:

a semiconductor substrate;

a first low-k dielectric layer overlying the semiconductor substrate with a first copper or copper alloy conductor embedded therein;

a second low-k dielectric layer overlying the first low-k dielectric layer;

a second conductor embedded in the second low-k dielectric layer and electrically connecting the first copper or copper alloy conductor, and the surface of the second low-k dielectric layer is lower than the surface of the second conductor; wherein the second conductor is composed of copper or copper alloy; and

a composite diffusion barrier layer formed by atomic layer deposition, interlaid between the second conductor and the second low-k dielectric layer.

11. The interconnect structure as claimed in claim 10 , further comprising a passivation layer overlying the second low-k dielectric layer and second conductor.

12. The interconnect structure as claimed in claim 11 , wherein the passivation layer comprises silicon carbide.

13. The interconnect structure as claimed in claim 11 , further comprising an etch-stop layer overlying the passivation layer.

14. The interconnect structure as claimed in claim 10 , further comprising a conductive passivation layer overlying the second conductor.

15. The interconnect structure as claimed in claim 10 , wherein the first low-k dielectric layer comprises silicon oxygen-containing material.

16. The interconnect structure as claimed in claim 10 , wherein the dielectric constant (k) of the first low-k dielectric layer is less than 2.8.

17. The interconnect structure as claimed in claim 10 , wherein the second low-k dielectric layer comprises silicon oxygen-containing material.

18. The interconnect structure as claimed in claim 10 , wherein the dielectric constant (k) of the second low-k dielectric layer is less than 2.8.

19. The interconnect structure as claimed in claim 10 , wherein the dielectric constant k of the second low-k dielectric layer is lower than that of the first low-k dielectric layer.

20. The interconnect structure as claimed in claim 10 , wherein the width of the second conductor is substantially from 200 to 100 Å.

21. The interconnect structure as claimed in claim 10 , further comprises a low-resistivity tantalum metal layer with a thickness from 10 to 100 Å, interlaid between the composite diffusion barrier layer and the second low-k dielectric layer.

22. The interconnect structure as claimed in claim 21 , wherein the low-resistivity metal layer is composed of a material selected from the group consisting of titanium and tantalum.

23. The interconnect structure as claimed in claim 10 , wherein the thickness of the composite diffusion barrier layer is from 30 to 300 Å.

24. The interconnect structure as claimed in claim 10 , wherein the composite diffusion barrier layer is composed of dual titanium nitride layers or dual tantalum nitride layers.

25. The interconnect structure as claimed in claim 10 , wherein the composite diffusion barrier layer is triply laminar of tantalum, tantalum nitride and tantalum.

26. The interconnect structure as claimed in claim 10 , wherein the surface of the second low-k dielectric layer is below the surface of the second conductor from 100 to 500 Å.

27. The interconnect structure as claimed in claim 10 , wherein the composite diffusion barrier layer comprises tantalum nitride.

28. The interconnect structure as claimed in claim 10 , wherein the composite diffusion barrier layer comprises titanium nitride.