Patent ID: 7414722

Claim:
An alignment measurement arrangement comprising: a broadband source arranged to generate a radiation beam with at least a first and second range of wavelengths; an optical system arranged to receive said radiation beam as generated, to produce an alignment beam, to direct said alignment beam to an alignment mark located on an object, to receive alignment radiation back from said at least one mark and to transmit said alignment radiation; a detector arranged to receive said alignment radiation and to detect an image of said alignment mark located on said object and to produce at least a first and second alignment signal for the alignment mark associated with said first and second range of wavelengths, respectively; and a processor connected to said detector wherein said processor is arranged to: receive said first and second alignment signal; determine a first and second signal quality respectively of said first and second alignment signal, respectively, by using at least one signal quality indicating parameter; establish a further alignment signal from said first and second alignment signal based on said first and second signal quality; and calculate a position of said alignment mark based on said further alignment signal.