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This is a technique for providing accurate overlay patterns by adjustin the field deflection of an E-beam system to match the field distortion of any optical system.
English (United States)
This text was extracted from a PDF file.
This is the abbreviated version, containing approximately
53% of the total text.
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Accurate Overlay between Patterns Written by E-Beam and Light Optical
This is a technique for providing accurate overlay patterns by adjustin the
field deflection of an E-beam system to match the field distortion of any optical
A scanning E-beam system is utilized as a tool for manufacturing
semiconductor devices by writing patterns to overlay other patterns which were
written previously by other E-beam systems or light optical means. The accuracy
with which patterns can overlay other patterns is determined not only by the E-
beam deflection accuracy, but also by the distortion of patterns to be overlayed
as they have been introduced by the optical systems. When patterns are written
by light optical systems, i.e., projecting patterns from masks to wafers, the
exposed pattern will suffer from field distortion imposed by lens distortion, etc.
One method is to calibrate the E-beam deflection to a calibration grid made
by the optical system to be compensated. Another method is to correlate the
measured E-beam deflection errors to a deflection similar to the distorted optical
field and generate corrections based on the difference.
The E-beam distortion is measured by scanning a calibration grid made of
holes in gold over silicon. Having previously characterized the grid so that the
relative position of the holes are known precisely, the true position of the beam
within the field is determined. Since the optical field distortion is basically a static
phenomena, it can be measured and determined. This distortion may be
represented as beam position shifts at every measurement point within the
deflection field of the E-beam system. These beam position shifts, due to optical
distortion, are then added to the characteristics of the reference target. The result
is a virtual reference target whose characteristics are the same as the optical