Endpoint detection for chemical mechanical polishing based on spectrometry
A method of detecting a polishing endpoint includes storing a plurality of library spectra, measuring a sequence of spectra from the substrate in-situ during polishing, and for each measured spectrum of the sequence of spectra, finding a best matching library spectrum from the plurality of library spectra to generate a sequence of best matching library spectra. Each library spectrum has a stored associated value representing a degree of progress through a polishing process, and the stored associated value for the best matching library spectrum is determined for each best matching library spectrum to generate a sequence of values representing a progression of polishing of the substrate. The sequence of values is compared to a target value, and a polishing endpoint is triggered when the sequence of values reaches the target value.
1. A method of controlling a chemical mechanical polishing operation, comprising:
storing a plurality of library spectra, each library spectrum of the plurality of library spectra having a stored associated value representing a degree of progress through a polishing process;
polishing a substrate;
measuring a sequence of spectra from the substrate in-situ during polishing;
for each measured spectrum of the sequence of spectra, finding a best matching library spectrum from the plurality of library spectra to generate a sequence of best matching library spectra;
for each best matching library spectrum from the sequence of best matching library spectra, determining the stored associated value for the best matching library spectrum to generate a sequence of values representing a progression of polishing of the substrate;
comparing the sequence of values to a target value; and
triggering a polishing endpoint when the sequence of values reaches the target value.
2. The method of claim 1 , wherein each library spectrum of the plurality of library spectra has a unique associated value.
3. The method of claim 1 , further comprising smoothing the sequence of values to generate a smoothed sequence and comparing comprises comparing the smoothed sequence to the target value.
4. The method of claim 1 , comprising sweeping a detection spot of an in-situ monitoring system across the substrate, measuring a plurality of spectra in each sweep of the detection spot across the substrate.
5. The method of claim 4 , comprising determining a radial zone on the substrate for each spectrum of the plurality of spectra in each sweep, and generating a sequence of values representing a degree of progress through a polishing process for each radial zone.
6. The method of claim 4 , wherein sweeping the detection spot comprises rotating a platen.
7. The method of claim 4 , comprising averaging a subset of the plurality of spectra from a sweep to provide a measured spectrum.
8. The method of claim 1 , wherein the sequence of values provides a trace, and respective stored associated values of the plurality of library spectra are substantially linearly proportional to a number of values at a point in a trace at which respective library spectra occur.
9. The method of claim 1 , wherein the plurality of library spectra are generated by measurement of spectra during polishing of a test substrate.
10. The method of claim 1 , wherein the plurality of library spectra are generated from theory.
11. The method of claim 1 , comprising applying a high-pass filter to each measured spectrum of the sequence of spectra.