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 chemical mechanical polishing system, comprising:
a support to hold a polishing pad;
a carrier head to hold a substrate against the polishing pad;
an in-situ optical monitoring system to measure a sequence of spectra during polishing; and
a controller configured to
store 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,
receive the sequence of spectra from the in-situ optical monitoring system,
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, determine 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;
compare the sequence of values to a target value, and
trigger a polishing endpoint when the sequence of values reaches the target value.
2. The system of claim 1 , wherein each library spectrum of the plurality of library spectra has a unique associated value.
3. The system of claim 1 , wherein the controller is configured to smooth the sequence of values to generate a smoothed sequence and to compare the smoothed sequence to the target value.
4. The system of claim 1 , wherein the in-situ optical monitoring system is configured to sweep a detection spot across the substrate and measuring a plurality of spectra in each sweep of the detection spot across the substrate, and the controller is configured to determine a radial zone on the substrate for each spectrum of the plurality of spectra in each sweep, and generate a sequence of values representing a degree of progress through a polishing process for each radial zone.
5. The system of claim 4 , wherein the support comprises a rotating platen and rotation of the platen sweeps the detection spot.
6. The system 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.
7. The system of claim 1 , wherein the controller is configured to receive measurements of a plurality of spectra during polishing of a test substrate and store the plurality of spectra as the library spectra.