Boundary layer model to account for thick mask effects in PhotoLithography

The lack of transparent optical components at short wavelengths limits the available wavelengths in Deep Ultraviolet lithography, while the required minimum feature on wafer continues to shrink towards deeper sub-wavelength scales. This places a serious limitation on Kirchhoff boundary conditions that replace the field on the mask openings by the incident field, since this approximation fails to account for the increasingly important topographical effects (thick mask effects) in the computation of the lithographic image. In this paper we present a sophisticated version of Kirchhoff approximation capable of modelling rigorous near field effects while retaining the simplicity of the scalar model. Our model is based on a comparison of the fields produced by both the thick and ideal thin masks on the wafer. Polarization and edge diffraction effects as well as phase and transmission errors, are included in our model.