High‐efficiency high‐repetition rate KrF excimer laser

Abstract

Abstract Discharge‐excited KrF excimer lasers with wavelength of 248 nm are expected to be useful as a light source for microlithography of 64‐Mbit DRAM. This paper reports on a high‐repetition‐rate UV preionized discharge‐excited KrF excimer laser with a new capacitor‐transfer‐circuit configuration in which peaking capacitors are buried in the wall of the laser vessel. This KrF laser delivers a high efficiency of 4 percent, a high average power of 150 W at 600 Hz, and a high‐repetition rate of 700 Hz. The gas lifetime has been confirmed to exceed 3 × 10 6 shots without a gas purifier. This paper also discusses oscillation efficiency, high‐repetition rate operations and the gas lifetime for KrF excimer lasers with an ultraviolet (UV) automatic preionization and a capacitor‐transfer circuit. It has been confirmed that long gas lifetime and high‐repetition rate have been achieved due to the high oscillation efficiency.