Photon tunneling microscopy (PTM) is an optical microscopy technique that c
an, by using frustrated total internal reflection, be sensitive to changes
in surface topography as small as 1 nm. We have developed a simple calibrat
ion technique that generates plots of sample reflectivity as a function of
topography. This empirical data is then used to convert a gray-scale image
of a specimen into an accurate topographic image. Errors, such as accurate
magnification calibration,and detector. nonlinearity, lead to only small di
fferences between the empirical data and our theoretical prediction. We hav
e used PTM to study the evolution of latent images in a chemically amplifie
d resist, ARCH2, as a function of dose, both after exposure and after poste
xposure bake, and have obtained good agreement between the topography measu
red in the PTM with thickness changes determined by ellipsometry from large
exposed areas. Comparison of the results of the PTM with those obtained by
near-field scanning optical microscopy demonstrate that changes in topogra
phy on the order of 3-5 nm are visible in the PTM. The topography that appe
ars to develop in a latent image is a function of feature size. This effect
occurs before the lateral resolution limit of the microscope is reached, a
nd is a result of the mechanical constraint arising from unexposed resist m
aterial around the exposed features. Techniques such as adjusting the polar
ization and wavelength of the illumination can improve the sensitivity of t
he technique to small changes in topography, while in the case of materials
that undergo changes in refractive index, contrast can be seen even in the
absence of topography. (C) 1998 American Vacuum Society. [S0734-211X(98)17
806-X].