Patent ID: 8593646
Filing Date: 2013-11-26
Classification: G01B,G02B,G03F

Abstract:
1. A method measuring a position of a mark on a substrate in an optical apparatus, the method comprising: providing a mark on the substrate; providing a measurement optical system comprising an illumination subsystem configured to illuminate the mark with a spot of radiation and a detecting subsystem configured to detect radiation diffracted by the mark; in a scanning operation moving the substrate and the measurement optical system relative to one another at a first velocity so as to scan the mark with the spot of radiation while detecting and processing signals representing the diffracted radiation to calculate a position of the mark relative to a reference frame of the measurement optical system; and synchronously with said scanning operation, moving the spot of radiation relative to the reference frame of the measurement optical system at a second velocity, the first and second velocities being related such that the spot scans the mark at a third velocity which is lower than the first velocity while said signals are detected.