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Local High Mag Scanning at Two Tail Ends of Low Mag Scanning For Creating High Mag SEM Stereo Images

IP.com Disclosure Number: IPCOM000121709D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 3 page(s) / 99K

Publishing Venue

IBM

Related People

Christenson, K: AUTHOR [+2]

Abstract

Disclosed is a method for creating a stereo pair of SEM images by doing a high-magnification raster scan at the tail end of a low-magnification field, and then mechanically moving the target or feature to the other extreme of the low-magnification field followed by another high-magnification raster scan. These two high-magnification raster scans form a "stereo pair". The reason why these two images form a stereo pair is explained below.

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Local High Mag Scanning at Two Tail Ends of Low Mag Scanning For
Creating High Mag SEM Stereo Images

      Disclosed is a method for creating a stereo pair of SEM
images by doing a high-magnification raster scan at the tail end of a
low-magnification field, and then mechanically moving the target or
feature to the other extreme of the low-magnification field followed
by another high-magnification raster scan.  These two
high-magnification raster scans form a "stereo pair".  The reason why
these two images form a stereo pair is explained below.

      In most Scanning Electron Microscopes (SEM), the beam always
goes through the center of the lens as it is rastered on the sample
(Figure 1).  While this form of scanning minimizes off-axis
aberrations such as coma, it also creates a perspective effect.
Features at the edge of the field appear to be tilted away from those
at the center (Figure 2).  The half angle dr of this tilt at a point
within an image is equal to arctan(dr/1), where dr is the distance
from the image center and 1 is the distance from the sample to the
pivot point (1 Z the lens' focal length).

      This perspective is much less pronounced at high magnifications
because high magnification images are taken by reducing the size of
the raster on the sample.  In this case, dr, and, hence, dr is small.

      Normally, the raster expands and contracts around a point on
the optic axis.  The microscope "zooms in" on the center of the
picture.

      If the raster is contracted around a feature near the edge of
the low magnification field, an image of the feature at high
magnification and (nearly) uniform tilt results. Mechanically moving
the feature to the opposite edge of the low magnification field and
repeating the procedure results in a high magnification image with
the opposite tilt.  Taken together, these images form a "stereo
pair"....