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.