Substrate and patterning device for use in metrology, metrology method and device manufacturing method

A method of measuring a parameter of performance of a lithographic process by which product features have been applied to a substrate, the method comprising:

• simultaneously applying the product features and metrology targets to the substrate, the metrology targets including a first set of targets distributed at locations across the substrate and a second set of targets which are for measuring the same parameter but which are smaller than the first set, the second set of targets including a first subset distributed at locations between the first set of targets, and a second subset distributed substantially at the same locations as the targets of the first set;
• illuminating the targets and detecting radiation diffracted or reflected by the targets and processing the radiation to determine values for the parameter at the locations of a plurality of the targets in each set;
• and
• correcting parameter values measured using the first subset of the second set of targets based on a comparison between values measured at one or more locations using a target of the second subset and a target of the first set.