International Business Machines Corporation

Ralph R Trotter

Samuel Kay Doran

Donald E Davis

Edward V Weber

Robert A Simpson

Donald F Haire

George W Cann

An electron beam is aligned with the center of an aperture in a plate in the path of the beam by cyclically scanning the beam across the aperture through equal distances on opposite sides of an initial beam location, measuring the beam current that flows through the aperture when the beam is on opposite sides of the initial location, which opposite sides correspond to adjacent half cycles of the scan, determining the difference in beam currents flowing in adjacent half cycles, and deflecting the beam in a direction toward the center of the aperture until there is reached a condition wherein the difference in currents is zero, which condition indicates that the beam is aligned with the center of the aperture. The currents may be measured by converting them to signals having a frequency proportional to the current, counting the signal cycles during each half cycle, and then subtracting the count for one half cycle from that of an adjacent half cycle. The amplitude of the scan is large enough such that the beam strikes the opposite edges of the aperture at the extreme limits of each scan. The scan frequency is preferably that of the power line frequency to eliminate noise problems. The total current flowing through the aperture during a complete scan cycle is also sensed and used to regulate the brightness of the electron beam.

Method and apparatus for controlling alignment and brightness of an

An alignment system for registration of a scanning beam in a mask inspection tool. Minimum scan widths (W) in the registration process are attained thereby increasing registration sensitivity. This technique allows initial placement of the E-Beam to be outside the capture range so that the scan on one side is completely off the metal (on glass) and the scan on the other side is completely on the metal. Correction signals are obtained by comparing the backscattered electron signals from the two scans with the magnitude of the signal being indicative of the amount of correction required and the sign being indicative of the direction of correction.

Alignment technique

An X-Y positioning system for electron beam lithography employs an adaptive drive system for feedback control. A gradually increasing drive voltage, superimposed upon a step wave, is summed with the position error signal to achieve position within the system deadband zone. The drive voltage, while superimposed upon the error voltage, increases until mechanical friction and drift in the deadband zone are overcome. A function generator alters the error signal such that the combined error signal and drive voltage cause the system to approach the null point minimizing servo oscillations. A limit circuit determines when the system has reached a set of inner limits and generates an operative output signal to the signal controller which continues until the position exceeds a second, outer set of limits.

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Hopewell Junction, NY, United States of America

Ralph R Trotter