Evaluation of Spectral Profiles of KrF Excimer Lasers for Microlithography

Abstract

A measuring method to evaluate the spectral profile of a KrF excimer laser used in lithography has been developed. In this method, the parameter of the spectral purity is defined by the spectral width of the laser (Δλ_95%E), which contains 95 % of its total energy. During the measurements, the instrumental function of a high-resolution spectrometer was precisely estimated with a single-mode laser. The deconvolution technique was applied to evaluate the spectral width of the laser from the observed spectrum by using the instrumental function and the influence on the deconvolved profiles, due to noises included in the observed spectra, was examined quantitatively. In order to keep the required measurement accuracy within ± 5 % of the value Δλ_95%E, the necessary product value of the maximum signal count-number and the signal averaging number was found to be more than 3.65×10⁶ in the present system.