Automatic beam correction in a scanning transmission electron mi

Details Automatic beam correction in a scanning transmission electron mi Automatic beam correction in a scanning transmission electron mi

1980-09-05

1983-04-05

Anderson, Bruce C.

Radiant energy

Inspection of solids or liquids by charged particles

Methods

250311, G01N 2300, H01J 3726

Patent

active

043792308

ABSTRACT:
In a scanning electron microscope, a periodic structure in the object plane is used for the detection of the focus condition of a spot-focussed electron beam scanning an object in order to correct defocusing and astigmatism in the scanning electron beam spot. To achieve this the detector comprises a plurality of individual elements which can be pair-wise read and an electronic circuit for forming a control signal for controlling the excitation of a spot-forming lens and a stigmator, respectively, from signals representing movement of the electron interference pattern at the detector, relative to the object scan, due to an out of focus condition. The signals are derived from corresponding pairs of detector elements which are situated at a fixed distance from each other in order to correct the focus and compensate for the astigmatism in the electron beam respectively. In the case of astimatism, signals from at least two pairs of detector elements spaced in directions at right-angles to one another, are used.

REFERENCES:
patent: 3576438 (1971-04-01), Pease
patent: 3833811 (1974-09-01), Koike et al.
patent: 4038543 (1977-07-01), Krisch et al.
patent: 4162403 (1979-07-01), Baumgarten
patent: 4214163 (1980-07-01), Namae et al.

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