Method and apparatus of eddy current monitoring for chemical mechanical polishing

1. A polishing system, comprising:

a polishing pad having a polishing surface;

a carrier to hold a substrate against the polishing surface of the polishing pad; and

an eddy current monitoring system including an induction coil positioned on a side of the polishing surface opposite the substrate, the induction coil extending at least partially through the polishing pad.

2. The polishing system of claim 1 , wherein the polishing pad includes a recess formed in a bottom surface thereof, and the coil is at least partially positioned in the recess.

3. The polishing system of claim 1 , wherein the coil is secured to the polishing pad.

4. The polishing system of claim 3 , wherein the coil is embedded in the polishing pad.

5. The polishing system of claim 1 , wherein the eddy current monitoring system includes a core, and the coil is wound about the core.

6. The polishing system of claim 1 , further comprising an optical monitoring system including a transparent window, and wherein the coil extends at least partially through the transparent window.

7. The polishing system of claim 1 , wherein the polishing pad is mounted on a top surface oh platen and the coil is supported by the platen.

8. A polishing system, comprising:

a polishing pad having a polishing surface;

a solid window situated at least partially in the polishing pad, the window having a recess;

a platen to which the polishing pad is attached;

a carrier to hold a substrate against the polishing surface of the polishing pad; and

an eddy current monitoring system including a ferromagnetic body positioned on a side of the polishing surface opposite the substrate, the ferromagnetic body extending at least partially through the polishing pad and partially into the recess, the ferromagnetic body being supported by the platen, wherein a gap separates the ferromagnetic body from the polishing pad.

9. The polishing system of claim 8 , wherein:

the polishing pad includes an aperture formed therethrough; and

dimensions of the window match dimensions of the aperture.

10. The polishing system of claim 8 , further comprising an optical monitoring system, the optical monitoring system including a light source operable to emit light, wherein the window is transparent to the light.

11. The polishing system of claim 8 , further comprising a coil wound around the ferromagnetic body.

12. The polishing system of claim 11 , wherein the coil extends at least partially through the polishing pad.

13. The polishing system of claim 8 , further comprising means for biasing the ferromagnetic body against the polishing pad.

14. The polishing system of claim 8 , wherein the ferromagnetic body is one of a rod shaped ferromagnetic body or a U-shaped ferromagnetic body.

15. A polishing system, comprising:

a polishing pad having a polishing surface;

a solid window situated at least partially in the polishing pad, the window having a recess;

a platen to which the polishing pad is secured;

a carrier to hold a substrate against the polishing surface of the polishing pad; and

an eddy current monitoring system including a core and a ferromagnetic body that is positioned on a side of the polishing surface opposite the substrate, the ferromagnetic body extending at least partially through the polishing pad and at least partially into the recess, the core being aligned with the ferromagnetic body when the polishing pad is attached to the platen.

16. The polishing system of claim 15 , wherein the ferromagnetic body is secured to the polishing pad.

17. The polishing system of claim 16 , wherein the ferromagnetic body is secured in the polishing pad with a polyurethane epoxy.

18. The polishing system of claim 16 , wherein the ferromagnetic body is embedded in the polishing pad.