Filtering during in-situ monitoring of polishing
A method of controlling polishing includes polishing a substrate, monitoring the substrate during polishing with an in-situ monitoring system, filtering a signal from the monitoring system to generate a filtered signal, and determining at least one of a polishing endpoint or an adjustment for a polishing rate from the filtered signal. The filtering includes modelling a plurality of periodic disturbances at a plurality of different frequencies using a plurality of disturbance states, modelling an underlying signal using a plant state, and applying a linear prediction filter to the plant state and the plurality of disturbance states to generate a filtered signal representing the underlying signal.
1. A computer program product for controlling a polishing system, the computer program product comprising a non-transitory computer-readable medium having instructions which when executed cause one or more computers to:
receive, during polishing of a substrate, a signal from an in-situ monitoring system of the polishing system, the signal including a sequence of measured values;
filter the signal to generate a filtered signal, the filtered signal including a sequence of adjusted values, wherein the instructions to filter the signal include instructions to
model a plurality of periodic disturbances, using a plurality of disturbance states, at a plurality of different frequencies,
model an underlying signal, using a plant state, and
apply a linear prediction filter to the plant state and the plurality of disturbance states to generate the filtered signal representing the underlying signal; and
cause the polishing system to at least one of halt polishing of the substrate or adjust a polishing rate of the substrate based on the filtered signal.
2. The computer program product of claim 1 , wherein the plurality of periodic disturbances consists of two periodic disturbances.
3. The computer program product of claim 1 , wherein the plurality of periodic disturbances consists of three periodic disturbances.
4. The computer program product of claim 1 , wherein the plurality of periodic disturbances include a head sweep disturbance.
5. The computer program product of claim 1 , wherein the instructions to filter the signal include instructions to model the underlying signal using a plurality of plant states.
6. The computer program product of claim 5 , wherein the plurality of plant states include a filtered motor current and a motor current rate.
7. The computer program product of claim 5 , wherein the plurality of plant states include a filtered torque and a torque rate.
8. The computer program product of claim 1 , wherein the linear prediction filter comprises a Kalman filter.
9. The computer program product of claim 1 , wherein the plurality of periodic disturbances include a platen rotation disturbance.
10. The computer program product of claim 1 , wherein the instructions to model the plurality of periodic disturbances comprise instructions to model the plurality of periodic disturbances as a plurality of sinusoids.
11. The computer program product of claim 1 , wherein the plurality of different frequencies are preset values.
12. The computer program product of claim 1 , wherein a frequency of the plurality of different frequencies is a variable in a model used for modeling the plurality of periodic disturbance.