Patent ID: 9551939
Date: 2017-01-24
CPC Classifications: G01B,G03F

Claim:
1. An apparatus comprising: an illumination arrangement to direct radiation with an illumination profile across a pupil of the apparatus, the illumination arrangement comprising an illumination source to provide multiple-wavelength radiation of substantially equal polarization and a wave plate to alter the polarization of the radiation in dependency of the wavelength, such that radiation of different wavelengths having different polarization is supplied; an objective lens to direct radiation on a mark using the radiation supplied by the illumination arrangement while scanning the radiation across the mark in a scanning direction; a radiation processing element to process radiation that is diffracted by the mark and received by the objective lens; and a detection arrangement to detect variation in an intensity of radiation output by the radiation processing element during the scanning and to calculate from the detected variation a position of the mark in at least a first direction of measurement.