Patent ID: 8294907

Claim:
A method of measuring one or more parameters of a plurality of target patterns which have been printed in one or more fields on a substrate by a lithographic process, the method comprising: directing an inspection beam of radiation onto a first one of the plurality of target patterns on the substrate and measuring radiation reflected or scattered therefrom to obtain first measurement data; processing the first measurement data to obtain a first value related to a parameter of the first one of the plurality of target patterns; directing the inspection beam of radiation onto a second one of the plurality of target patterns on the substrate and measuring radiation reflected or scattered therefrom to obtain second measurement data; processing the second measurement data to obtain a second value related to a parameter of the second one of the plurality of target patterns on the substrate, wherein in the processing the second measurement data a seed value derived from the first value is used to assist in obtaining the second value, and wherein the processing the first measurement data and the processing the second measurement data comprise a search of a library space, the library space constructed based on a random error range of the seed value.