Substrate polishing metrology using interference signals
A method of polishing a substrate includes holding the substrate on a polishing pad with a polishing head, wherein the polishing pad is supported by a platen, creating relative motion between the substrate and the polishing pad to polish a side of the substrate, generating a light beam and directing the light beam towards the substrate to cause the light beam to impinge on the side of the substrate being polished. Light reflected from the substrate is at a detector to generate an interference signal. A measure of uniformity is computed from the interference signal.
1. A method of polishing a substrate, comprising:
holding the substrate on a polishing pad with a polishing head, wherein the polishing pad is supported by a platen;
creating relative motion between the substrate and the polishing pad to polish a side of the substrate;
generating a light beam;
directing the light beam towards the substrate to cause the light beam to impinge on the side of the substrate being polished;
receiving light reflected from the substrate at a detector to generate a time-varying interference signal; and
computing a measure of uniformity from the interference signal based on a difference between the time-varying interference signal and a time-varying base signal.
2. The method of claim 1 , wherein creating relative motion includes rotating the polishing head.
3. The method of claim 2 , wherein creating relative motion includes rotating the platen.
4. The method of claim 3 , wherein the light beam is a laser beam.
5. The method of claim 1 , further comprising:
comparing the measure of uniformity to a reference; and
generating an alert when the measure of uniformity diverges from the reference by more than a predetermined amount.
6. A method of polishing a substrate, comprising:
holding the substrate on a polishing pad with a polishing head, wherein the polishing pad is supported by a platen;
creating relative motion between the substrate and the polishing pad to polish a side of the substrate;
generating a light beam;
directing the light beam towards the substrate to cause the light beam to impinge on the side of the substrate being polished;
receiving light reflected from the substrate at a detector to generate an interference signal; and
displaying a characterizing waveform for an operator to see, the characterizing waveform presenting data for a period of time that extends over multiple cycles of the interference signal.
7. The method of claim 6 , wherein creating relative motion includes rotating the polishing head.
8. The method of claim 7 , wherein creating relative motion includes rotating the platen.
9. The method of claim 8 , wherein a laser interferometer generates the light beam and receives the light reflected from the substrate.
10. The method of claim 6 , further comprising:
receiving from an operator input indicating two points on the waveform;
computing a frequency from the two points on the waveform;
generating filter coefficients from the frequency;
using the filter coefficients to generate one or both of a low frequency signal or a high frequency signal from the interference signal; and
computing a measure of uniformity from one or both of the low frequency signal or the high frequency signal.