STI CMP under polish monitoring

1. A method comprising:

depositing an oxide over a semiconductor wafer;

reducing the oxide from a portion of the semiconductor wafer by performing chemical mechanical polishing (CMP) above a pad nitride layer proximate a shallow trench isolation (STI) region; and

deducing a thickness of oxide remaining at a location within the portion using scatterometric metrology.

2. The method according to claim 1 , comprising deducing the thickness by:

calculating scattering spectra for a plurality of oxide thicknesses, producing calculated scattering spectra;

monitoring scattering spectra at the location within the portion of the semiconductor wafer;

comparing the monitored scattering spectra at the location to the calculated scattering spectra;

determining a closest matching calculated scattering spectra to the monitored scattering spectra at the location; and

obtaining an oxide thickness corresponding to the closest matching calculated scattering spectra.

3. The method according to claim 2 , wherein reducing the oxide comprises hydrogen fluoride (HF) deglazing.

4. The method according to claim 2 , wherein the location is within a static random access memory (SRAM) portion on the semiconductor wafer.

5. The method according to claim 2 , wherein the location is over dummy structures formed on the semiconductor wafer.

6. The method according to claim 2 , comprising:

monitoring scattering spectra at one to ten locations per die of the semiconductor wafer;

comparing the monitored scattering spectra at each location to the calculated scattering spectra;

determining a closest matching calculated scattering spectra to the monitored scattering spectra at each location; and

obtaining an oxide thickness corresponding to the closest matching calculated scattering spectra for each location.

7. The method according to claim 1 , wherein the oxide comprises a high aspect ratio process (HARP) oxide.

8. The method according to claim 1 , further comprising increasing a time for CMP based on a deduced thickness of remaining oxide greater than zero.

9. The method according to claim 8 , comprising repeating the steps of increasing a time for CMP and deducing a thickness until the deduced thickness is zero.

10. A method comprising:

calculating scattering spectra for each of a plurality of oxide thicknesses, producing calculated scattering spectra;

associating the scattering spectra with the corresponding oxide thickness;

creating a library of scattering spectra and associated oxide thicknesses;

providing an oxide layer on a semiconductor wafer;

reducing a thickness of the oxide layer on a portion of the semiconductor wafer, forming a reduced oxide layer, wherein reducing the thickness of the oxide comprises performing chemical mechanical polishing (CMP) above a pad nitride layer proximate a shallow trench isolation (STI) region;

measuring scattering spectra of the reduced oxide layer;

accessing the library of scattering spectra;

determining a calculated scattering spectra that matches the measured scattering spectra of the reduced oxide layer;

obtaining the associated oxide thickness of the calculated scattering spectra that matches the measured scattering spectra of the reduced oxide layer; and

repeating the steps of reducing, measuring, accessing, determining, and obtaining until the obtained oxide thickness is zero.

11. The method according to claim 10 , wherein the oxide comprises a high aspect ratio process (HARP) oxide.

12. The method according to claim 10 , comprising measuring scattering spectra within a static random access memory (SRAM) portion on the semiconductor wafer.

13. The method according to claim 10 , comprising measuring scattering spectra over dummy structures formed on the semiconductor wafer.

14. A method comprising:

calculating scattering spectra for each of a plurality of oxide thicknesses, producing calculated scattering spectra;

associating the scattering spectra with the corresponding oxide thickness;

creating a library of scattering spectra and associated oxide thicknesses;

providing an oxide layer on a semiconductor wafer;

reducing a thickness of the oxide layer on a portion of the semiconductor wafer, forming a reduced oxide layer;

measuring scattering spectra of the reduced oxide layer at up to 10 locations per die across the portion of the semiconductor wafer;

accessing the library of scattering spectra;

determining a calculated scattering spectra that matches the measured scattering spectra of the reduced oxide layer at each of the multiple locations;

obtaining the associated oxide thickness of each calculated scattering spectra that matches a measured scattering spectra of the reduced oxide layer;

identifying a zone in which an obtained oxide thickness is greater than zero;

reworking the identified zone; and

repeating the steps of measuring, accessing, determining, and obtaining until no obtained oxide thickness is greater than zero.

15. The method according to claim 14 , comprising reducing the oxide thickness by chemical mechanical polishing (CMP).

16. The method according to claim 14 , wherein the oxide layer comprises a high aspect ratio process (HARP) oxide.

17. The method according to claim 14 , comprising measuring scattering spectra within a static random access memory (SRAM) portion on the semiconductor wafer or over dummy structures formed on the semiconductor wafer.