Reduction of Acoustic Waves Induced by Discharge in High Repetition Rate ArF Excimer Laser Cavity to Obtain Narrow-Bandwidth Laser Light

The suppression of acoustic waves caused by discharge in a laser chamber, which is a technical challenge we face in the development of next-generation 6 kHz ArF lasers for lithography, is studied. In this paper, we describe, firstly, that the acoustic waves produced in an ArF laser medium were observed by a Schlieren method and analyzed by computer simulation. The simulation results successfully explained the gas density fluctuation pattern obtained in Schlieren photographs. On the basis of these results, the inner configuration of a laser chamber for 6-kHz-repetition-rate operation was newly designed. The new laser chamber provided narrow-bandwidth laser light up to a repetition rate of 6 kHz as a result of a marked suppression of acoustic waves.