Polishing with pre deposition spectrum

1. A computer program product, encoded on one or more non-transitory computer storage media, comprising instructions that when executed by one or more computers cause the one or more computers to perform operations comprising:

storing a base spectrum, the base spectrum being a spectrum of light reflected from a substrate after deposition of a plurality of deposited dielectric layers overlying a metallic layer or semiconductor wafer and before deposition of a non-metallic layer over the plurality of deposited dielectric layers;

after deposition of the non-metallic layer over the plurality of deposited dielectric layers and during polishing of the non-metallic layer on the substrate, receiving from an in-situ optical monitoring system measurements of a sequence of raw spectra of light reflected from the substrate during polishing;

normalizing each raw spectrum in the sequence of raw spectra to generate a sequence of normalized spectra using the raw spectrum and the base spectrum; and

determining at least one of a polishing endpoint or an adjustment for a polishing rate based on at least one normalized predetermined spectrum from the sequence of normalized spectra.

2. The computer program product of claim 1 , wherein the base spectrum comprises a spectrum of the substrate measured after deposition of the dielectric layers but before an etching process, after the etching process but before deposition of a nitride layer, or after deposition of the nitride layer but before depositing the non-metallic layer undergoing polishing.

3. The computer program product of claim 1 , wherein normalizing comprises a division operation in which the raw spectrum is in a numerator and the base spectrum is in a denominator.

4. The computer program product of claim 3 , wherein the division operation comprises calculating

R

=

A

-

D

A

B

-

D

B

where R is the normalized spectrum, A is the raw spectrum, B is the base spectrum and D A and D B are dark spectra, the one or more dark spectra being measured by the in-situ optical monitoring system when no substrate is being measured by the in-situ optical monitoring system.

5. The computer program product of claim 1 , wherein the operations further comprise generating a sequence of values from the sequence of normalized spectra, fitting a function to the sequence of values, determining a projected time at which the function reaches a target value, and determining at least one of the polishing endpoint or the adjustment for the polishing rate based on the projected time.

6. The computer program product of claim 5 , wherein the operations further comprise:

for each normalized spectrum from the sequence of normalized spectra, finding a best matching reference spectrum from a library having a plurality of reference spectra, and wherein generating the sequence of values includes determining a value associated with each best matching reference spectrum.

7. The computer program product of claim 6 , wherein the operations further comprise halting the polishing when the function matches or exceeds the target value.

8. The computer program product of claim 1 , wherein polishing the substrate comprises a back-end-of-line portion of an integrated circuit fabrication process.

9. A method of fabricating a substrate comprising:

depositing at least one dielectric layer on a metallic layer or semiconductor wafer of the substrate;

measuring a base spectrum reflected from the substrate, at an optical metrology system, after depositing the at least one dielectric layer but before depositing an outermost layer;

depositing the outermost layer on the at least one dielectric layer;

polishing the outermost layer of the substrate;

during polishing of the outermost layer, measuring a sequence of raw spectra reflected from the substrate, at an in-situ optical monitoring system;

normalizing each raw spectrum in the sequence of raw spectra to generate a sequence of normalized spectra using the raw spectrum and the base spectrum; and

determining at least one of a polishing endpoint or an adjustment for a polishing rate based on at least one normalized predetermined spectrum from the sequence of normalized spectra.

10. The method of claim 9 , comprising

depositing alternating non-metallic layers onto the substrate, the alternating non-metallic layers including the at least one dielectric layer;

etching the substrate to create a staircase structure;

depositing an intermediate layer onto the etched substrate; and

depositing the outermost layer onto the intermediate layer.

11. The method of claim 10 , wherein measuring the base spectrum comprises measuring the base spectrum after depositing the alternating non-metallic layers onto the substrate but before etching the substrate, the alternating non-metallic layers comprising alternating oxide and nitride layers.

12. The method of claim 10 , wherein measuring the base spectrum comprises measuring the base spectrum after etching the substrate but before depositing a nitride layer.

13. The method of claim 10 , wherein measuring the base spectrum comprises measuring the base spectrum after depositing a nitride layer but before depositing the outermost layer.

14. An integrated circuit fabrication system, comprising:

a deposition system configured to receive a substrate, and deposit a stack of layers overlying a metallic layer or semiconductor substrate, the stack of layers including a non-metallic layer to undergo polishing and at least one dielectric layer underlying the non-metallic layer;

a metrology system configured to generate a measurement of a spectrum of light reflected from the substrate after deposition of the at least one dielectric layer and before deposition of the non-metallic layer; and

a polishing system configured to receive the substrate and polish the non-metallic layer on the substrate, wherein the polishing system includes a controller configured to

receive the measurement of the spectrum of light from the metrology system and store the measurement as a base spectrum,

receive measurements of a sequence of raw spectra of light reflected from the substrate during polishing with an in-situ optical monitoring system,

normalize each raw spectrum in the sequence of raw spectra to generate a sequence of normalized spectra using the raw spectrum and the base spectrum, and

determine at least one of a polishing endpoint or an adjustment for a polishing rate based on at least one normalized predetermined spectrum from the sequence of normalized spectra.

15. The system of claim 14 , wherein the base spectrum comprises a spectrum of the substrate measured after deposition of the at least one dielectric layer but before an etching process, after the etching process but before deposition of a nitride layer, or after deposition of the nitride layer but before depositing the non-metallic layer undergoing polishing.

16. The system of claim 14 , wherein the metrology system is an in-line metrology station in the deposition system.

17. The system of claim 14 , wherein the metrology system is a stand-alone metrology system.

18. A polishing system comprising:

a carrier configured to mount a substrate, wherein the substrate includes a stack of layers overlying a metallic layer or semiconductor substrate, the stack of layers including a non-metallic layer undergoing polishing and a plurality of deposited dielectric layers underlying the non-metallic layer;

a platen to receive a polishing pad configured to be in contact with the substrate;

an in-situ optical monitoring system; and

a controller configured to

store a post deposition base spectrum, the post deposition base spectrum being a spectrum of light reflected from the substrate after deposition of the plurality of deposited dielectric layers and before deposition of the non-metallic layer;

receive, from the in-situ optical monitoring system, measurements of a sequence of raw spectra of light reflected from the substrate during polishing;

normalize each raw spectrum in the sequence of raw spectra to generate a sequence of normalized spectra using the raw spectrum and the post deposition base spectrum; and

determine at least one of a polishing endpoint or an adjustment for a polishing rate based on at least one normalized predetermined spectrum from the sequence of normalized spectra.

19. A computer program product, encoded on one or more non-transitory computer storage media, comprising instructions that when executed by one or more computers cause the one or more computers to perform operations comprising:

storing a base measurement, the base measurement being an eddy current measurement of a substrate after deposition of at least one layer overlying a semiconductor wafer and before deposition of a conductive layer over the at least one layer;

after deposition of the conductive layer over the at least one layer and during polishing of the conductive layer on substrate, receiving a sequence of raw measurements of the substrate from an in-situ eddy current monitoring system;

normalizing each raw measurement in the sequence of raw measurement to generate a sequence of normalized measurements using the raw measurement and the base measurement; and

determining at least one of a polishing endpoint or an adjustment for a polishing rate based on at least the sequence of normalized measurements.