Wave front sensor with grey filter and lithographic apparatus comprising same
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United States of America Patent
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Jun 17, 2008
Grant Date -
Dec 20, 2007
app pub date -
Jun 15, 2006
filing date -
Jun 15, 2006
priority date (Note) -
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Abstract
A radiation distribution measurement system for measuring a phase distribution of a beam of radiation and/or a pupil distribution of a projection system includes a transparent carrier plate, a grating and/or a pinhole configured at a first side of the transparent carrier plate, and a camera at an opposite side of the transparent carrier plate. The measurement system also includes a radiation filter between the transparent carrier plate and the camera, with a transmissivity that is lowest at the center of the filter and gradually and concentrically increases towards the outside of the filter. By placing the filter with its specific transmissivity, the difference in intensity across the wave front sensor 10 (i.e. the gradient in intensity) is compensated. The intensity of the light incident on the camera is made more uniform resulting in an improved performance of the measurement system.
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