Abstract: Exemplary methods for detecting substrate slippage include sweeping a first sensor and a second sensor of an in-situ monitoring system across the substrate as the substrate undergoes polishing with a rotatable platen. A first sequence of signal values from the first sensor and a second sequence of signal values from the second sensor include a signal strength relative to the thickness of the layer. For each signal value of at least some of the first sequence of signal values and second sequence of signal values, the method may include determining a first and second position on the substrate respective. The method may also include activating a slippage alert if: the signal strength varies by 30% or more from the first sequence of signal values to the second sequence of signal values, a position on the substrate for the second signal value cannot be determined, or a combination thereof.

Abstract: Exemplary methods for detecting substrate slippage include sweeping a first sensor and a second sensor of an in-situ monitoring system across the substrate as the substrate undergoes polishing with a rotatable platen. A first sequence of signal values from the first sensor and a second sequence of signal values from the second sensor include a signal strength relative to the thickness of the layer. For each signal value of at least some of the first sequence of signal values and second sequence of signal values, the method may include determining a first and second position on the substrate respective. The method may also include activating a slippage alert if: the signal strength varies by 30% or more from the first sequence of signal values to the second sequence of signal values, a position on the substrate for the second signal value cannot be determined, or a combination thereof.