Two-wavelength anti-reflection coating for ArF excimer laser lithography optics

Abstract

In ArF excimer laser lithography optics, two wavelengths are used for different purposes. One is for exposure, and the other is for through-the-lens alignment. Hence, we studied an anti-reflection coating functioning at two wavelengths simultaneously. At first, 2- and 3-layer dielectric thin-films were designed just for the exposure wavelength (lambda=193 nm), and the performance analysis and optimization of the reflectance at the alignment wavelength (lambda=488 nm) followed. The transmittance dependency on the incident angle was analyzed at both wavelengths. The uniformity of the transmittance in lithography optics over the range of incident angles is as important as low reflectance in attaining uniform intensity distribution in the exposure field. The best of our designs was the [air/CaF2/LaF3/BaF2/substrate] structure, considering the deposition errors. This design showed uniform transmittance and low reflectance over the range of +/-30 degrees for the incident angles.