Browse Prior Art Database

Automatic Method for Aligning Optical Components in a Charged Particle Optical System

IP.com Disclosure Number: IPCOM000101861D
Original Publication Date: 1990-Sep-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Chang, THP: AUTHOR [+3]

Abstract

Disclosed is a method for automatically centering a source or limiting aperture in a charged particle system with respect to the optical axis. This process can occur dynamically without disturbing the system operation.

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This is the abbreviated version, containing approximately 82% of the total text.

Automatic Method for Aligning Optical Components in a Charged Particle Optical System

       Disclosed is a method for automatically centering a
source or limiting aperture in a charged particle system with respect
to the optical axis.  This process can occur dynamically without
disturbing the system operation.

      By wobbling the optical component with respect to the optical
axis, small variations in the beam current will occur.  The variation
in beam current can be detected at the target or at a limiting
aperture using a lock-in amplifier. The component can be wobbled by
using x and y mechanical transducers, such as piezoelectrics driven
by sinusoidal signals. This would be an arrangement similar to that
used to center a scanning tunneling microscope tip over a specific
feature on a sample (*).  Although the figure shows a source being
driven in a circular motion with the signal being detected by a
dual-phase lockin amplifier, separate frequencies in x and y could
also be applied to the optical component.  Two single-channel lock-in
amplifiers would then be used to detect the signal, one locked to the
x frequency and one locked to the y frequency.

      In operation, when a component is off center, it produces a
signal in the beam current whose phase indicates the direction of
error. This phase information is used to automatically center the
component using a simple set of analog electronics that send a signal
to the same mechanical transducer that pe...