EVALUATION OF THE WAVE-GUIDE EFFECT IN PROXIMITY X-RAY-LITHOGRAPHY USING AN OPTICAL TRACE METHOD

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.