Measurements of beam characteristics relevant to DUV microlithography on a KrF excimer laser

Abstract

We present measurements of several optical characteristics of the 248 nm beam produced by a spectrally narrowed KrF excimer laser designed for the deep ultraviolet reduction stepper. These measurements include intensity divergence and polarization profiles spectral content and coherence properties. Using a special high resolution spectrometer we have established an upper limit of 2. 27 pm FWHM for the spectral bandwidth in agreement with measurements made with a diagnostic etalon. We have also found that the wavelength varies across the horizontal profile of the beam at a linear rate of 0. 59 pm/mm. No comparable wavelength variation is seen in the vertical direction. Coherence measurements show that the vertical and horizontal spatial coherence lengths are different 60 mm and 126 mm respectively. The temporal coherence length is 33. 3 mm in good agreement with the measured bandwidth. 1.