Patent ID: 7046367
Filing Date: 2006-05-16
Classification: G01B,G03F,G05B

Abstract:
1. A method comprising: a) positioning a stage relative to energy used to expose a sample supported by the stage; b) measuring values of a distance measuring interferometry signal indicative of the relative position of the stage for a first period of time; c) using the values from the first period of time to determine one or more correction factors for the distance measuring interferometry signal, wherein the correction factors relate to cyclic errors in a distance measuring interferometer used to produce the distance measuring interferometry signal; d) measuring at least one value of the distance measuring interferometry signal during a second period of time following the first period of time; e) correcting the value from the second period of time based on the correction factors; and f) using the corrected values from the second period of time to improve the relative positioning of the stage.