T. Ogawa et al., EVALUATION OF THE WAVE-GUIDE EFFECT IN PROXIMITY X-RAY-LITHOGRAPHY USING AN OPTICAL TRACE METHOD, JPN J A P 2, 34(5B), 1995, pp. 644-647
In proximity X-ray lithography, mask-patterns may be 500 to 1000 times
as thick as the X-ray wavelength. This suggests the occurrence of phy
sical phenomena such as interference between wave modes propagating th
rough a mask pattern. Change in intensity profiles of X-rays caused by
such interference, referred to as the waveguide effect, is re-evaluat
ed through a new simulation method. This simulation uses a technique b
ased oil the optical trace method to superpose rays that can propagate
the mask pattern. As a result. the influence of the waveguide effect
can be calculated for the mask pattern consisting of not only a perfec
t conductor but also a real material. The feasibility of this simulati
on is investigated by comparing the intensity profiles of X-rays with
those obtained using a previous simulation method based on Maxwell's e
quations with a mask pattern assumed to be a perfect conductor. The re
sults suggest that the new simulation is applicable for wide mask patt
ern sizes ranging from 500 nm (0.5 mu m) to below 100 nm (0.1 mu m). T
he simulation results also show that the waveguide effect makes intens
ity profiles of X-rays propagated through a 50-nm-wide mask pattern of
tungsten (W) narrower than the pat tern width. Furthermore, the energ
y of X-rays propagated through this mask pattern is found tc, decrease
about 12%. These results indicate that the waveguide effect influence
s the intensity profiles of X-rays propagated through the mask pattern
, even if it consists of real materials.