Method and structure for interconnection

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

forming a first low-k dielectric layer over a substrate;

forming a first and second metal features in the first low-k dielectric layer;

forming a first trench in the first low-k dielectric layer, the first trench spanning between the first and second metal features;

performing a ultraviolet (UV) treatment to sidewalls of the first low-k dielectric layer in the first trench;

forming a first etch stop layer in the first trench; and

depositing a second low-k dielectric layer on the first etch stop layer, thereby forming an air gap in the first trench.

2. The method of claim 1 , wherein the forming of the first and second metal features in the first low-k dielectric layer includes

patterning the first low-k dielectric layer, thereby forming second trenches in the first low-k dielectric layer;

filling the second trenches with a metal material; and

performing a polishing to the metal material, thereby forming the first and second metal features.

3. The method of claim 1 , wherein the forming the first trench in the first low-k dielectric layer includes

forming, on the first low-k dielectric layer, an etch mask having an opening; and

etching the first low-k dielectric layer through the opening, thereby forming the first trench that spans from the first metal feature to the second metal feature in a first direction and spans between the sidewalls of the first low-k dielectric layer in a second direction being different from the first direction.

4. The method of claim 1 , wherein the forming of first trench in the first low-k dielectric layer includes:

forming a second etch stop layer over the first and second metal features and the first low-k dielectric layer;

patterning the second etch stop layer to form an opening in the second etch stop layer, wherein the opening exposes the first low-k dielectric layer in a region between the first and second metal features;

performing a dry etching process to the first low-k dielectric layer through the opening, using a fluorine-containing etchant; and

performing a wet etching process to the first low-k dielectric layer through the opening.

5. The method of claim 1 , wherein the performing of the UV treatment to the sidewalls of the first low-k dielectric layer is prior to the forming of the first etch stop layer and after the forming of the first trench in the first low-k dielectric layer.

6. The method of claim 1 , wherein the performing of the UV treatment to the sidewalls of the first low-k dielectric layer includes

irradiating an UV radiation on to the sidewalls of the first low-k dielectric layer; and

supplying a first gas containing a CH 3 chemical group to the first low-k dielectric layer during the irradiating of the UV radiation.

7. The method of claim 6 , wherein the supplying of the first gas containing the CH 3 chemical group includes supplying a gas selected from the group consisting of a methylsilane (SiCH 6 ), dimethylsilane (SiC 2 H 8 ), a trimethylsilan (SiC 3 H 10 ), a tetramethylsilane (SiC 4 H 12 ) and a combination thereof.

8. The method of claim 7 , wherein the irradiating of the UV radiation to the sidewalls of the first low-k dielectric layer includes applying an UV radiation source having a spectrum to effectively break Si—CH 3 bond and O—H bond.

9. The method of claim 6 , wherein the performing of the UV treatment to the sidewalls of the first low-k dielectric layer further includes supplying a second gas to carry on the first gas to the sidewalls of the first low-k dielectric layer, wherein the second gas is an inert gas selected from the group consisting of nitrogen and argon.

10. The method of claim 1 , wherein the forming of the first etch stop layer includes forming the first etch stop layer conformal to the first trench.

11. The method of claim 1 , further comprising a chemical mechanical polishing process to the second low-k dielectric layer after the depositing of the second low-k dielectric layer on the first etch stop layer.

12. A method of fabricating a semiconductor structure, comprising:

forming a first low-k dielectric layer over a substrate;

forming a first and second metal features in the first low-k dielectric layer;

forming a first trench in the first low-k dielectric layer, the first trench spanning between the first and second metal features;

irradiating an UV radiation to sidewalls of the first trench in the first low-k dielectric layer;

supplying a first gas containing a CH 3 chemical group to the first low-k dielectric layer during the irradiating of the UV radiation;

forming a first etch stop layer in the first trench; and

depositing a second low-k dielectric layer on the first etch stop layer, thereby forming an air gap in the first trench.

13. The method of claim 12 , wherein the supplying of the first gas containing the CH 3 chemical group includes supplying a gas selected from the group consisting of a methylsilane (SiCH 6 ), dimethylsilane (SiC 2 H 8 ), a trimethylsilan (SiC 3 H 10 ), a tetramethylsilane (SiC 4 H 12 ) and a combination thereof.

14. The method of claim 13 , wherein the irradiating of the UV radiation to the sidewalls of the first low-k dielectric layer includes applying an UV radiation source having a spectrum to effectively break Si—CH 3 bond and O—H bond.

15. The method of claim 13 , further comprising supplying a second gas to carry on the first gas to the sidewalls of the first low-k dielectric layer during the irradiating of the UV radiation, wherein the second gas is an inert gas selected from the group consisting of He, Ne, Ar, Kr, Xe, Rn, or a combination thereof.

16. The method of claim 12 , further comprising heating the semiconductor structure to a temperature ranging between 200° C. and 400° C., during the irradiating of the UV radiation.

17. The method of claim 12 , wherein the irradiating of the UV radiation includes

irradiating a first UV radiation form a first UV source with a first UV spectrum to effectively break a Si—C bond of the first gas;

irradiating a second UV radiation from a second UV source with a second spectrum to effectively break an O—H bond of the low-k dielectric layer, wherein the second spectrum is different from the first spectrum.

18. The method of claim 17 , wherein

the first UV spectrum of the first radiation has a first central frequency greater than the bond energy of the Si—CH 3 bond at about 310 KJ/mol; and

the second UV spectrum of the first radiation has a first central frequency greater than the bond energy of the O—H bond at about 459 KJ/mol.

19. A method of fabricating a semiconductor structure, comprising:

forming a first low-k dielectric layer over a substrate;

forming a first and second metal features in the first low-k dielectric layer;

forming a first trench in the first low-k dielectric layer, the first trench spanning between the first and second metal features;

performing a ultraviolet (UV) treatment to sidewalls of the first low-k dielectric layer in the first trench;

thereafter, forming a first etch stop layer in the first trench; and

depositing a second low-k dielectric layer on the first etch stop layer, thereby forming an air gap in the first trench, wherein the UV treatment includes

irradiating an UV radiation to the sidewalls of the first low-k dielectric layer;

supplying a first gas containing a CH 3 chemical group to the first low-k dielectric layer during the irradiating of the UV radiation; and

heating the semiconductor structure to a temperature ranging between 200° C. and 400° C., during the irradiating of the UV radiation.

20. The method of claim 19 , wherein the irradiating of the UV radiation to the sidewalls of the first low-k dielectric layer includes

irradiating a first UV radiation form a first UV source with a first UV spectrum to effectively break a Si—C bond of the first gas;

irradiating a second UV radiation from a second UV source with a second spectrum to effectively break an O—H bond of the first low-k dielectric layer, wherein the second spectrum is different from the first spectrum.