Stacked interconnect structure and method of making the same

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

forming a first dielectric layer overlying a first conductive layer;

etching a trench opening in the first dielectric layer;

depositing a sacrificial material layer in the trench opening;

forming a second conductive layer overlying the sacrificial material layer;

forming an etch stop layer over the second conductive layer;

etching away portions of the etch stop layer and the second conductive layer to provide a second conductive portion over the first conductive layer, and an etch stop that overlies the second conductive portion;

forming a second dielectric layer overlying the etch stop layer and the sacrificial material layer;

forming a via to the sacrificial material layer; and

performing an etch to remove the sacrificial material layer through the via and leave a resultant air gap between the first conductive layer and the second conductive layer decreasing the effective dielectric constant between the first and second conductive layers, and decreasing the RC time constant of the interconnect structure.

2. The method of claim 1 , further comprising forming a third dielectric layer over the sacrificial material layer prior to forming the second conductive layer.

3. The method of claim 1 , further comprising forming an intermediate layer in between the sacrificial material layer and the second dielectric layer.

4. The method of claim 3 , wherein the performing an etch to remove the sacrificial material layer through the via further comprises concurrently etching a second via to the second conductive portion stopping on the etch stop layer.

5. The method of claim 4 , further comprising performing an etch to remove the etch stop down to the second conductive layer.

6. The method of claim 1 , wherein the etch stop layer is titanium nitride (TiN).

7. The method of claim 2 , wherein forming the second conductive layer further comprises forming the second dielectric layer over the third dielectric layer and the second conductive layer.

8. The method of claim 1 , wherein the first dielectric layer is porous silicon carbide hydroxide (SiCOH).

9. The method of claim 1 , wherein the performing an etch to remove the sacrificial material layer comprises performing a vapor phase etch.

10. The method of claim 1 , wherein the sacrificial material layer is polysilicon and the etch employs a Xenon Fluoride (XeF 2 ) gas.

11. A method of forming an interconnect structure, the method comprising:

forming a first dielectric layer overlying a first conductive layer;

etching a trench opening in the first dielectric layer;

depositing a sacrificial material layer in the trench opening;

forming a second conductive layer overlying the sacrificial material layer;

forming an etch stop layer over the second conductive layer;

etching away portions of the etch stop layer and the second conductive layer to provide a second conductive portion over the first conductive layer, and an etch stop that overlies the second conductive portion;

forming a third dielectric layer overlying the etch stop layer and the sacrificial material layer;

performing an etch to concurrently form a first via to the sacrificial material layer and a second via to the etch stop of the second conductive portion; and

performing an etch to remove the sacrificial material layer through the first via and leave a resultant air gap between the first conductive layer and the second conductive portion decreasing the effective dielectric constant between the first conductive layer and the second conductive portion.

12. The method of claim 11 , further comprising performing an etch to remove the etch stop down to the second conductive layer.

13. The method of claim 11 , wherein the etch stop layer is titanium nitride (TiN).

14. The method of claim 11 , wherein each of the first dielectric layer, a second dielectric layer and the third dielectric layer are porous silicon carbide hydroxide (SiCOH).