Endpointing 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 computer program product, tangibly embodied in a non-transitory computer readable medium, comprising instructions for causing a computer to perform operations 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;
receiving, from an in-situ monitoring system, a sequence of spectra from a substrate 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 an amount of progression of the substrate through the polishing process;
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 computer program product of claim 1 , wherein each library spectrum of the plurality of library spectra has a unique associated value.
3. The computer program product of claim 1 , wherein the operations further comprise smoothing the sequence of values to generate a smoothed sequence and comparing comprises comparing the smoothed sequence to the target value.
4. The computer program product 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.