Pressure signals during motor torque monitoring to provide spatial resolution
A method of polishing includes holding a substrate with a carrier head against a polishing surface of a polishing pad, generating relative motion between the substrate and polishing pad, applying a first pressure modulated by a first modulation function to a first region of the substrate, applying a second pressure modulated by a second modulation function that is orthogonal to the first modulation function to a second region of the substrate, during polishing of the substrate monitoring the substrate with an in-situ friction monitoring system to generate a sequence of measured values, and determining a relative contribution to the sequence of measured value from the first region and second region based on distinguishing the first frequency from the second frequency.
1. A computer program product, comprising a non-transitory computer-readable medium having instructions to cause one or more computers to:
cause a carrier head of a polishing system to apply a first pressure modulated by a first modulation function to a first region of a substrate during polishing of the substrate;
cause the carrier head of the polishing system to apply a second pressure modulated by a second modulation function that is orthogonal to the first modulation function to a different second region of the substrate;
receive a sequence of measured values from an in-situ friction monitoring system;
determine a relative contribution to the sequence of measured value from the first region and second region based on distinguishing the first modulation function from the second modulation function;
determine which of the first region or the second region an overlying layer is clearing first to expose an underlying layer; and
adjust a polishing parameter based on which of the first region or the second region is clearing first.
2. The computer program product of claim 1 , wherein the first modulation function comprises a first cyclic waveform having a first frequency and the second modulation function comprises a second cyclic waveform having a different second frequency.
3. The computer program product of claim 1 , comprising storing one or more parameters indicating a relative coefficient of friction of the overlying layer and the underlying layer.
4. The computer program product of claim 3 , wherein storing the one or more parameters comprises storing a single parameter indicating which of the overlying layer and the underlying layer has a higher coefficient of friction.
5. The computer program product of claim 3 , wherein storing the one or more parameters comprises storing a first parameter indicating a coefficient of friction of the overlying layer and a second parameter indicating a coefficient of friction of the underlying layer.
6. The computer program product of claim 3 , comprising instructions to determine a scalar projection of the sequence of measured values onto each of the first modulation function and the second modulation function to generate a first value and a second value.
7. The computer program product of claim 6 , wherein the one or more parameters indicate that the underlying layer has a lower coefficient of friction, and comprising instructions to determine that the first region is clearing before the second region based on the first value decreasing relative to the second value.
8. The computer program product of claim 6 , wherein the one or more parameters indicate that the underlying layer has a higher coefficient of friction, and comprising instructions to determine that the first region is clearing before the second region based on the first value increasing relative to the second value.
9. The computer program product of claim 6 , wherein the one or more parameters indicate that the underlying layer has a lower coefficient of friction, and comprising instructions to determine that the second region is clearing before the first region based on the second value decreasing relative to the first value.
10. The computer program product of claim 6 , wherein the one or more parameters indicate that the underlying layer has a higher coefficient of friction, and comprising instructions to determine that the second region is clearing before the first region based on the second value increasing relative to the first value.
11. The computer program product of claim 1 , comprising instructions to receive a first nominal pressure and a second nominal pressure from a polishing recipe, and wherein an average of the first pressure modulated by the first modulation function equals the first nominal pressure and an average of the second pressure modulated by the second modulation function equals the second nominal pressure.
12. The computer program product of claim 11 , comprising instructions to compute a first upper pressure value and a first lower pressure value based on the first nominal pressure and a second upper pressure value and a second lower pressure value based on the second nominal pressure.