Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Patent
1989-03-31
1990-12-18
Anderson, Bruce C.
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
250307, 250397, H01J 3726
Patent
active
049788566
ABSTRACT:
In an automatic focusing apparatus according to the invention, a focusing lens is provided for focusing an electron beam which scans a specimen. Charged particles emanating from the specimen are then detected. The excitation current energizing the lens is varied in accordance with a sweep signal that changes linearly. The electron beam scans at each different value of the sweep signal. An evaluating signal is produced indicating the degree to which the focusing lens is focused. The excitation current supplied to the lens is set according to the output signal from the evaluating signal-producing means. The linearly swept excitation current is modulated with a periodic signal. Plural cases are determined where the evaluating signal assumes maximum values. In each case, the average value of the linearly swept signal is calculated. The excitation current is set to a value to be supplied to the focusing lens, corresponding to the average value. The focusing lens is energized with electric current having the set value to focus the beam onto the specimen.
REFERENCES:
patent: 3937959 (1976-02-01), Namae
patent: 4169240 (1979-09-01), Anderson et al.
patent: 4199681 (1980-02-01), Namae
patent: 4393309 (1983-07-01), Norioka
patent: 4464680 (1984-08-01), Yamanaka
patent: 4514634 (1985-04-01), Lawson
Anderson Bruce C.
Jeol Technics Co.
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