Level sensor arrangement in a lithographic apparatus for measuring multi-layer surfaces

摘要

Disclosed is a method of measuring a position of at least one substantially reflective layer surface on a substrate in a lithographic apparatus, and associated level sensor and lithographic apparatuses. The method comprises performing at least two interferometrical measurements using a broadband light source. Between each measurement, the component wavelengths and/or intensity levels over the component wavelengths of the broadband source beam is varied such that, where it is only the intensity levels that are varied, the intensity variation is different for at least some of the beam's component wavelengths. Alternatively, a single measurement and subsequent processing of the measurement to obtain measurement data whereby the component wavelengths and/or intensity levels over the component wavelengths are different can be applied as well to obtain the position.

主权项

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.