NARROW BAND GAS DISCHARGE LASER WITH GAS ADDITIVE

摘要

The present invention provides a very narrow band pulse excimer laser capabl e of producing pulses at a rate in the range of about 500 to 2000 Hz with enhanced energy dose control and repoducibility. Very small quantities of a stabilizing additive consisting of oxygen or a heavy noble gas (xenon or rad on for KrF lasers, or krypton, xenon or radon for ArF lasers), are added to the gas mixture. Tests performed show substantial improvements in energy stabili ty with the addition of about 30 ppm of xenon to a KrF laser. Tests show improv ed performance for the ArF Lasers with the addition of about 6-10 ppm of Xe or 40 ppm of Kr. In a preferred embodiment, very narrow bandwidth is achieved on a KrF laser by reducing fluorine partial pressure to less than 0.10 percent an d by increasing the reflectance of the output coupler to greater than 25 percent. In a preferred embodiment, prior art fused silica beam expansion prisms used in the prior art line narrowing module were replaced with calciu m fluoride prisms (see fig - specification devoid of reference numeros).