Ikuo Hikima

Spatial coherence of KrF excimer lasers

The spatial coherence and the beam divergence at 248 nm of a KrF excimer laser were obtained experimentally. These results are in good agreement with the theoretical calculations based on a simple pulse-laser model and the van Cittert-Zernike theorem. The relation between the spatial coherence and the beam divergence was obtained theoretically and supported by experimental results. This expression is given as a function of the wavelength of the laser but includes no parameters related to the laser structure. It is shown that these theoretical results are applicable to various kinds of pulse laser.

Illumination System Of An Excimer Laser Stepper

An illumination system suitable for an excimer laser stepper has been investigated. Unnecessary interference pattern(speckel) is reduced effectively by scanning the laser beam. We report spatial coherence of the lasers with different spectral line width, illumination system of the stepper, appearance of the interference pattern,its spacing and contrust and their relation to the illumination system and to the coherence of the laser. Then we report reduction of this pattern together with a simple method to measure its contrast.