Method for astigmatism correction in charged particle beam systems
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United States of America Patent
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-
Feb 15, 2000
Grant Date -
N/A
app pub date -
May 29, 1998
filing date -
May 29, 1998
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A method for calculating and correcting an astigmatism error in a charged particle beam system. Images are collected during a single focus sweep of the charged particle beam system. Different orientations of image features, such as lines on a stigmation target, are analyzed. Optimum sharpness or best focus values are obtained as a function of the objective lens settings. Appropriate changes to the settings of the astigmatism correctors are computed by taking a linear combination of optimum sharpness values associated with the different orientations of image features. Proper settings of the objective lens and the astigmatism correctors result in focusing of the beam into a 'small' spot. In a scanning electron microscope, for example, two sets of quadrupole compensation coils are typically used as astigmatism correctors.
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