Method for centering a lens in a charged-particle system

Radiant energy – With charged particle beam deflection or focussing – With target means

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250396R, 2504922, H01J 37147

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057478147

ABSTRACT:
A method for improving the alignment of an electron-beam through the optical axis of lenses in a lithographic system is described. The beam is nominally tilted through the center of the lens, and by using a plurality of deflectors the beam is pivoted through the center of the lens using a square wave toggle. The resolution of the beam is measured as it scans over a target, for both toggle states. The nominal tilt angle is chosen such that the resolution is identical for both toggle states. This technique does not rely on using an observation station, as it is common on TEMs, to view a magnified image of the specimen. Therefore, this technique can be used to align a beam that has been shifted off the optical axis, for instance, in a Variable-Axis-Lens lithography (VAL) system.

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