Determining substrate precession with acoustic signals

A chemical mechanical polishing system, comprising:

• polishing station including a platen to support a polishing pad;
• a rotatable carrier head to hold a surface of a substrate against the polishing pad;
• a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate;
• an in-situ acoustic monitoring system comprising an acoustic sensor that receives acoustic signals from the surface of the substrate;
• and
• a controller configured to determine a rate of change of angular orientation of the substrate based on received acoustic signals from the in-situ acoustic monitoring system, to obtain a rotation rate of the carrier head, and to determine a difference in angular orientation between the substrate and the carrier head based on the rate of change of angular orientation of the substrate and the rotation rate of the carrier head.

A chemical mechanical polishing apparatus, comprising:

• a platen to support a polishing pad;
• a carrier head to hold a surface of a substrate against the polishing pad;
• a notch detector arranged in the carrier head;
• a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate;
• an in-situ acoustic monitoring system comprising an acoustic sensor that receives acoustic signals from the surface of the substrate;
• and
• a controller configured to determine an angular orientation of the substrate based on a signal from the notch detector and on received acoustic signals from the in-situ acoustic monitoring system.