Automatic electron beam alignment and astigmatism correction in scanning electron microscope
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United States of America Patent
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May 6, 1997
Grant Date -
N/A
app pub date -
Jun 17, 1996
filing date -
Jun 17, 1996
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A border of a circular specimen defining a high contrast feature is imaged. Multiple border portions are sampled at a magnification showing each portion as a straight edge. For alignment a location indicator signal is generated at each of minimum and maximum focal range. Image translation is detected from the two signals, and alignment automatically adjusted. The process repeats for subsequent border portions at a 90.degree. interval until image translation falls for a sample is less than a threshold. For astigmatism correction border portions are sampled about the entire specimen circumference at a 30.degree. interval. An axis of beam distortion is identified based upon a maximum image translation axis among the samples. Distortion is adjusted along such axis. Then, astigmatism connection signal strength is indexed and astigmatism correction is repeated iteratively until correction for a current iteration is less than a given threshold.
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