Patent ID: 9279657
Filing Date: 2016-03-08
CPC Classification: G01B,G03F

Claim Text:
1. A method of measuring a position of at least one substantially reflective layer surface on a substrate in a lithographic apparatus, the method comprising performing: separating a broadband source beam of radiation into a reference beam and a measurement beam by respectively reflecting part of the broadband source beam off a first partly transparent optical element and passing part of the broadband source beam through the first partly transparent optical element; reflecting the measurement beam off the substrate to obtain a first reflected measurement beam; reflecting the measurement beam off of a surface of a second partly transparent optical element to obtain a second reflected measurement beam; passing the reference beam through the second partly transparent optical element and reflecting the reference beam off a reflective surface to obtain a reflected reference beam; combining the second reflected measurement beam and the reflected reference beam; and detecting at least two different interference patterns of the combined beams, wherein the different interference patterns are based on combined beams having at least one of different component wavelengths and intensity levels over a subset of the component wavelengths.