Talbot effect immersion lithography by self-imaging of very fine grating patterns

Talbot effect immersion lithography was investigated to improve resolution based on simulation results. The resolution limit of typical projection optics is determined by the wavelength λ of the light source and the numerical aperture. Alternatively, the Talbot effect forms self-images with no projection optics. For our simulations, the authors proposed using a mask with a Cr pattern illuminated by 193 nm ArF laser. The authors also assumed that the gap under the mask was filled with high-index immersion fluid of n = 1.64. The finite difference time domain (FDTD) optical simulation is shown for various pitches from 110 to 200 nm. So far, the distance of the self-imaging period has been estimated by second-order approximation, but the estimated result is found to differ significantly from the FDTD result. The periodic distance from low-order diffractive rays should be estimated by a higher-order approximation or an analytical method. Using Talbot effect immersion lithography, the one-dimensional line-and-space pattern of 60 nm pitch and the two-dimensional contact hole of 70 nm pitch can be transferred by a 193 nm light source.