Alignment system and methods for lithographic systems using at least two wavelengths

Abstract

An alignment system for a lithographic apparatus has a source of alignment radiation that has a first wavelength and a second wavelength; a detection system that has a first wavelength channel arranged to receive alignment radiation from an alignment mark at the first wavelength and a second wavelength channel arranged to receive alignment radiation from the alignment mark at the second wavelength; and a position determining unit in communication with the detection system. The position determining unit processes information from the first and second wavelength channels in combination to determine a position of the alignment mark based on information from the first wavelength channel, information from the second wavelength channel or combined information from the first and second wavelength channels according to a relative strength of the alignment radiation detected at the first wavelength to alignment radiation detected at the second wavelength. A lithographic apparatus includes the above alignment system. Methods of alignment and manufacturing devices use the above alignment system and lithographic apparatus, respectively.