Alignment sensor, lithographic apparatus and alignment method

Abstract

Disclosed is an alignment sensor comprising, and associated method comprising an illumination source, such as a white light source, having an illumination grating operable to diffract higher order radiation at an angle dependent on wavelength; and illumination optics to deliver the diffracted radiation onto an alignment grating from at least two opposite directions. For every component wavelength incident on the alignment grating, and for each direction, the zeroth diffraction order of radiation incident from one of the two opposite directions overlaps a higher diffraction order of radiation incident from the other direction. This optically amplifies the higher diffraction orders with the overlapping zeroth orders.

Description

[0001] Cross References to Related Applications [0002] This application claims priority to US Provisional Application 61 / 820,568, filed May 7, 2013, which is hereby incorporated by reference in its entirety. technical field [0003] The present invention relates to an alignment sensor and an alignment method, such as those used in photolithography processes. Background technique [0004] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus may be used, for example, in the manufacture of integrated circuits (ICs). In this case, a patterning device, alternatively called a mask or reticle, may be used to create the circuit pattern to be formed on the individual layers of the IC. The pattern can be transferred onto a target portion (eg, a portion comprising one or several dies) on a substrate (eg, a silicon wafer). The transfer of the pattern is usually done via imagi...

AI Technical Summary

Problems solved by technology

However, in dark field detection, these orders add up, making it impossible to detect asymmetry

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