Non-feature-dependent focusing

Details Non-feature-dependent focusing Non-feature-dependent focusing

2007-02-06

2007-02-06

Vanore, David A. (Department: 2881)

Radiant energy

Inspection of solids or liquids by charged particles

Methods

Reexamination Certificate

active

11020586

ABSTRACT:
One embodiment disclosed relates to an automated process for focusing a charged-particle beam in an apparatus onto an area of a substrate. A focusing parameter of the apparatus is set to a value, and intensity data is acquired from the area. The foregoing setting and acquiring steps are repeated for a range of values for the focusing parameter. A focusing sharpness measure is computed for each value of the focusing parameter based on noise in the acquired intensity data, and an in-focus value is determined for the focusing parameter based on the computed focusing sharpness measures. The focusing parameter of the apparatus may be, for example, an objective lens current, or a substrate bias voltage. The computation of the noise-based focusing sharpness measure may involve generating shifted or interleaved signals and calculating correlations between these signals. The focusing may be advantageously performed on an area lacking substantial edge information.

REFERENCES:
patent: 5130540 (1992-07-01), Yamada et al.
patent: 6025600 (2000-02-01), Archie et al.
patent: 6753518 (2004-06-01), Watanabe et al.

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