Patent ID: 7066785

Claim:
A polishing apparatus comprising: a rotatable turntable having a polishing pad; a carrier head configured to cooperate with the polishing pad to hold a target workpiece to be polished in alignment with the polishing pad on the turntable; and a magnetic field control unit comprising a plurality of spaced apart first magnetic field sources disposed inside the carrier head, for generating respective first magnetic forces, and a plurality of second magnetic field sources disposed inside the carrier head configured to generate respective second magnetic forces with each second magnetic field source comprising an electromagnet, a respective one of the plurality of second magnetic field sources being substantially spatially aligned with a respective one of the first magnetic field sources to define a magnetic field source pair, each magnetic field source pair being spaced apart from the others, wherein, in operation, the second magnetic field source in each magnetic field source pair is configured to selectively repel or attract the first magnetic field source such that, in operation, polarity of at least one of said electromagnets can reverse, and wherein, during operation, electromagnets in adjacent magnetic field source pairs have opposing polarity.