CD-AFMs (critical dimension atomic force microscopes) are instruments with servo-control of the tip in
more than one direction. With appropriately "boot-shaped" or flared tips, such instruments can image
vertical or even undercut features. As with any AFM, the image is a dilation of the sample shape with the
tip shape. Accurate extraction of the CD requires a correction for the tip effect. Analytical methods to
correct images for the tip shape have been available for some time for the traditional (vertical feedback
only) AFMs, but were until recently unavailable for instruments with multi-dimensional feedback. Dahlen
et al. [J. Vac. Sci. Technol. B23, pp. 2297-2303, (2005)] recently introduced a swept-volume approach,
implemented for 2-dimensional (2D) feedback. It permits image simulation and sample reconstruction,
techniques previously developed for the traditional instruments, to be extended for the newer tools. We
have introduced [X. Qian and J. S. Villarrubia, Ultramicroscopy, in press] an alternative dexel-based
method, that does the same in either 2D or 3D. This paper describes the application of this method to
sample shapes of interest in semiconductor manufacturing. When the tip shape is known (e.g., by prior
measurement using a tip characterizer) a 3D sample surface may be reconstructed from its 3D image.
Basing the CD measurement upon such a reconstruction is shown here to remove some measurement
artifacts that are not removed (or are incompletely removed) by the existing measurement procedures.