  Near-field phase-shifting contact lithography is modeled to characterize
electromagnetic absorption in a photoresist layer with one face in contact with
a quartz binary phase-shift mask. The broadband ultraviolet illumination is
represented as a frequency-spectrum of normally incident plane waves. A
rigorous coupled-wave analysis is carried out to determine the absorption
spectrum of the photoresist layer. The specific absorption rate in the
photoresist layer is calculated and examined in relation to the geometric
parameters. Columnar features in the photoresist layer are of higher quality on
broadband illumination in contrast to monochromatic illumination, in conformity
with some recent experimental results. Feature resolution and profile are
noticeably affected by the depth of the grooves in the phase-shift mask.
Ideally, the feature linewidth can be less than about 100 nm for broadband
illumination in the transverse-magnetic mode. These conclusions are subject to
modification by the photochemistry-wavelength characteristics of the
photoresist.
