High-resolution transmission electron microscopy (HR-TEM) has been
used as the ultimate method of thickness measurement for thin films.
The appearance of phase contrast interference patterns in HR-TEM images
has long been confused as the appearance of a crystal lattice by
nonspecialists. Relatively easy to interpret crystal lattice images are
now directly observed with the introduction of annular dark-field
detectors for scanning TEM (STEM). With the recent development of
reliable lattice image processing software that creates crystal
structure images from phase contrast data, HR-TEM can also provide
crystal lattice images. The resolution of both methods has been
steadily improved reaching now into the sub-Ångstrom region.
Improvements in electron lens and image analysis software are
increasing the spatial resolution of both methods. Optimum resolution
for STEM requires that the probe beam be highly localized. In STEM,
beam localization is enhanced by selection of the correct aperture.
When STEM measurement is done using a highly localized probe beam,
HR-TEM and STEM measurement of the thickness of silicon oxynitride
films agree within experimental error. In this article, the optimum
conditions for HR-TEM and STEM measurement are discussed along with a
method for repeatable film thickness determination. The impact of
sample thickness is also discussed. The key result in this article is
the proposal of a reproducible method for film thickness
determination.