Js. Kim et al., 2-WAVELENGTH ANTIREFLECTION COATING FOR ARF EXCIMER-LASER LITHOGRAPHYOPTICS, Journal of the Korean Physical Society, 33(2), 1998, pp. 136-142
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 funct
ioning at two wavelengths simultaneously. At first, 2- and 3-layer die
lectric thin-films were designed just for the exposure wavelength (lam
bda=193 nm), and the performance analysis and optimization of the refl
ectance at the alignment wavelength (lambda=488 nm) followed. The tran
smittance dependency on the incident angle was analyzed at both wavele
ngths. The uniformity of the transmittance in lithography optics over
the range of incident angles is as important as low reflectance in att
aining uniform intensity distribution in the exposure field. The best
of our designs was the [air/CaF2/LaF3/BaF2/substrate] structure, consi
dering the deposition errors. This design showed uniform transmittance
and low reflectance over the range of +/-30 degrees for the incident
angles.