Polishing interconnect structures in semiconductor devices

1. A method, comprising:

forming a first conductive feature over a semiconductor substrate;

forming an interlayer dielectric (ILD) layer over the first conductive feature;

patterning the ILD layer to form a trench;

forming a conductive layer over the patterned ILD layer to fill the trench;

polishing the conductive layer to form a via contact configured to interconnect the first conductive feature with a second conductive feature, wherein polishing the conductive layer exposes a top surface of the ILD layer;

polishing the exposed top surface of the ILD layer, such that a top portion of the via contact protrudes from the exposed top surface of the ILD layer; and

forming the second conductive feature over the via contact, such that the top portion of the via contact extends into the second conductive feature.

2. The method of claim 1 , wherein polishing the conductive layer includes performing a first chemical-mechanical polishing (CMP) process, and wherein the first CMP process implements a first CMP slurry.

3. The method of claim 2 , wherein polishing the exposed top surface of the ILD layer includes performing a second CMP process followed by a third CMP process, wherein the second CMP process implements a second CMP slurry, wherein the third CMP process implements a third CMP slurry, and wherein the first CMP slurry, the second CMP slurry, and the third CMP slurry include different compositions.

4. The method of claim 3 , wherein a pH of the first CMP slurry is lower than pH of the second CMP slurry and pH of the third CMP slurry.

5. The method of claim 3 , wherein the third CMP process removes the ILD layer at a greater rate than the second CMP process.

6. The method of claim 1 , wherein polishing the conductive layer forms a concave profile in the top portion of the via contact, and wherein polishing the exposed top surface of the ILD layer forms a convex profile in the top portion of the via contact.

7. The method of claim 1 , wherein forming the first conductive feature includes forming a source/drain contact or forming a metal gate stack.

8. A method, comprising:

forming a conductive feature over a semiconductor substrate;

forming a first interlayer dielectric (ILD) layer over the conductive feature;

patterning the first ILD layer;

depositing a conductive layer over the patterned first ILD layer;

performing a first chemical-mechanical polishing (CMP) process to the conductive layer, thereby forming a first interconnect feature having a dishing profile at top surface, wherein the first interconnect feature is configured to electrically couple the conductive feature with a second interconnect feature;

planarizing the first interconnect feature, comprising:

performing a second CMP process to remove a first portion of the first ILD layer; and

performing a third CMP process to remove a second portion of the first ILD layer disposed below the first portion, wherein performing the third CMP process removes the dishing profile;

forming a second ILD layer over the first interconnect feature, wherein a top portion of the first interconnect feature is embedded in the second ILD layer; and

forming the second interconnect feature in the second ILD layer.

9. The method of claim 8 , wherein depositing the conductive layer includes depositing a tungsten-containing material.

10. The method of claim 9 , wherein performing the first CMP process implements a catalyst for oxidizing the tungsten-containing material.

11. The method of claim 8 , wherein performing the first CMP process, the second CMP process, and the third CMP process include implementing a first slurry having a first pH, a second slurry having a second pH, and a third slurry having a third pH, respectively, wherein the first pH is less than the second pH, and wherein the second pH is less than the third pH.

12. The method of claim 11 , wherein the first slurry is configured to promote oxidation of the conductive layer, and wherein the second slurry and the third slurry are configured to suppress oxidation of the conductive layer.

13. The method of claim 8 , wherein the second CMP process removes the first portion of the first ILD layer at a first rate and the third CMP process removes the second portion of the first ILD layer at a second rate, and wherein the first rate is less than the second rate.

14. The method of claim 8 , wherein forming the second interconnect feature includes forming the second interconnect feature on the first interconnect feature, such that the top portion of the first interconnect feature protrudes into the second interconnect feature.

15. A semiconductor structure, comprising:

a conductive feature disposed over a semiconductor substrate;

a first interlayer dielectric (ILD) layer disposed over the conductive feature;

a first interconnect feature disposed in the first ILD layer, wherein the first interconnect feature extends to below a top surface of the conductive feature;

a second ILD layer disposed over the first ILD layer; and

a second interconnect feature disposed in the second ILD layer, wherein the first interconnect feature couples the conductive feature to the second interconnect feature, wherein a top surface of the second interconnect feature is above a top surface of the second ILD layer, and wherein a top portion of the first interconnect feature extends into the second interconnect feature.

16. The semiconductor structure of claim 15 , wherein the conductive feature includes a source/drain contact disposed over the semiconductor substrate.

17. The semiconductor structure of claim 16 , wherein the conductive feature is a first conductive feature, the semiconductor structure further comprising:

a second conductive feature disposed over the semiconductor substrate and under the first interlayer dielectric (ILD) layer;

a third conductive feature disposed adjacent to the second conductive feature; and

a butted contact disposed in the first ILD layer and configured to couple the second conductive feature with the third conductive feature, wherein a top portion of the butted contact extends into the second ILD layer.

18. The semiconductor structure of claim 17 , wherein the top portion of the first interconnect feature has a first thickness and the top portion of the butted contact has a second thickness, and wherein the second thickness is greater than the first thickness.

19. The semiconductor structure of claim 17 , wherein the top portion of the butted contact is more leveled with respect to a top surface of the first ILD layer than the top portion of the first interconnect feature or the second interconnect feature.

20. The semiconductor structure of claim 15 , wherein the top portion of the first interconnect feature is defined by a convex profile.