Automatic electron beam alignment and astigmatism correction in

Details Automatic electron beam alignment and astigmatism correction in Automatic electron beam alignment and astigmatism correction in

1996-06-17

1997-05-06

Berman, Jack I.

Radiant energy

Inspection of solids or liquids by charged particles

Electron probe type

250391R, 250396ML, H01J 37252

Patent

active

056273738

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.

REFERENCES:
patent: 3852597 (1974-12-01), Yanaka et al.
patent: 4494000 (1985-01-01), Shii et al.

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