Patent ID: 9360770
Filing Date: 2016-06-07
CPC Classification: G03F

Claim Text:
1. A method of determining focus corrections for a lithographic projection apparatus, the method comprising: measuring a focus dependent characteristic for each of a plurality of intrafield correction marks on a test substrate, wherein the intrafield correction marks are arranged in a plurality of intrafield correction fields, the intrafield correction marks having been exposed using varying focus; determining intrafield focus variation information for each intrafield correction mark location from the measured focus dependent characteristic; calculating the intrafield focus corrections from the intrafield focus variation information while taking into account scan-up-scan-down effects and grid plate focus errors induced as a result of a grid plate forming part of the lithographic apparatus, wherein the calculating intrafield focus corrections comprises modeling the different intrafield focus variation information using a filter to filter out a particular region of the test substrate.