Chemical mechanical polishing process

1. A chemical mechanical polishing process, comprising:

placing a substrate on a first polishing pad of a first platen, wherein the substrate has a bulk metal layer and a barrier layer;

polishing the bulk metal layer by using the first polishing pad having a hardness of above 50 (Shore D) until the barrier layer is exposed;

after removing the bulk metal layer, polishing the barrier layer on a second polishing pad of a second platen, wherein the second polishing pad has a hardness ranging between 40 and 50 (Shore D) and comprises an upper layer and a lower backing layer and said upper layer has a hardness less than 50 (Shore D).

2. The chemical mechanical polishing process according to claim 1 , wherein polishing the barrier layer is done by dispersing an alkaline condition chemical onto the second polishing pad.

3. The chemical mechanical polishing process according to claim 2 , wherein the alkaline condition chemical comprises triethanolamine, ethylene glycol, piperazine (C 4 H 10 N 2 ), and citric acid.

4. The chemical mechanical polishing process according to claim 2 , wherein the alkaline condition chemical has a pH of about 9.0 to 11.0.

5. The chemical mechanical polishing process according to claim 1 , wherein the second polishing pad has a compressibility of about 0.5% to 4.0%.

6. The chemical mechanical polishing process according to claim 1 , wherein the second polishing pad has thereon a transparent window for thickness measurement.

7. The chemical mechanical polishing process according to claim 1 , further comprising:

periodically rejuvenating a polishing surface of the second polishing pad using a conditioning diamond disk.

8. A chemical mechanical polishing process, comprising:

providing a substrate having a bulk metal layer and a barrier layer;

polishing the substrate with a first polishing pad on a first platen to substantially remove an upper portion of the bulk metal layer, wherein the first polishing pad has a hardness of above 50 (Shore D);

polishing the substrate with a second polishing pad on a second platen to remove the residual bulk metal layer, thereby exposing the barrier layer, wherein the second polishing pad has a hardness of above 50 (Shore D); and

polishing the substrate with a third polishing pad on a third platen to remove the barrier layer, wherein the third polishing pad has a hardness ranging between 40 and 50 (Shore D) and comprises an upper layer and a lower backing layer and said upper layer has a hardness less than 50 (Shore D).

9. The chemical mechanical polishing process according to claim 8 , wherein the upper layer has a hardness of 40 to 50 (Shore D).

10. The chemical mechanical polishing process according to claim 8 , wherein the third polishing pad has a compressibility of about 0.5% to 4.0%.

11. The chemical mechanical polishing process according to claim 8 , further comprising:

periodically rejuvenating a polishing surface of the third polishing pad using a conditioning system and condition chemicals.

12. The chemical mechanical polishing process according to claim 11 , wherein the condition chemicals comprise triethanolamine, ethylene glycol, piperazine (C 4 H 10 N 2 ), and citric acid.

13. The chemical mechanical polishing process according to claim 11 , wherein the condition chemicals have a pH of about 9.0 to 11.0.

14. The chemical mechanical polishing process according to claim 8 , wherein lifetime of the third polishing pad is monitored by a closed-loop control.

15. The chemical mechanical polishing process according to claim 14 , wherein the closed-loop control is established by a thickness measurement system that connects to the third platen.

16. The chemical mechanical polishing process according to claim 8 , wherein the third polishing pad has thereon a transparent window.