METHOD AND APPARATUS FOR MEASURING ASYMMETRY OF A MICROSTRUCTURE, POSITION MEASURING METHOD, POSITION MEASURING APPARATUS, LITHOGRAPHIC APPARATUS AND DEVICE MANUFACTURING METHOD

摘要

A lithographic apparatus includes an alignment sensor including a self-referencing interferometer for reading the position of an alignment target comprising a periodic structure. An illumination optical system for focusing radiation into a spot on said structure. An asymmetry detection optical system receives a share of positive and negative orders of radiation diffracted by the periodic structure, and forms first and second images of said spot on first and second detectors respectively, wherein said negative order radiation is used to form the first image and said positive order radiation is used to form the second image. A processor for processing together signals from said first and second detectors representing intensities of said positive and negative orders to produce a measurement of asymmetry in the periodic structure. The asymmetry measurement can be used to improve accuracy of the position read by the alignment sensor.

主权项

1. An apparatus for method of measuring an asymmetry dependent parameter of a periodic structure on a substrate, the apparatus comprising:
an illumination optical system for focusing radiation into a spot on said structure; first and second detectors of radiation; a detection optical system for receiving radiation diffracted by the periodic structure, including at the same time both positive and negative higher orders of diffracted radiation, and forming first and second images of said spot on first and second detectors respectively, wherein said negative order radiation is used to form the first image and said positive order radiation is used to form the second image; and a processor for processing together signals from said first and second detectors representing intensities of said positive and negative orders to produce a measurement of said asymmetry dependent parameter in the periodic structure.