The polarization induced by the mask is studied by using a 3D rigorous model, which solves Maxwell equations using the finite element method. The aerial image depends strongly on the change of polarization induced by the materials, thickness of the layer and pitch of the periodic masks.
Through ArF immersion lithography a road towards increased optical resolution at the 193nm wavelength has been opened. According to recently proposed roadmaps, ArF immersion lithography will be used for 65nm and 45nm technology nodes. Consequently, keeping the same 4x optical demagnification factor, the dimensions on mask scale down to wavelength values when entering these nodes. Moreover CD control becomes tighter and approaches values of 2-3nm. At such conditions, topography on mask, its type and materials cannot be ignored anymore while evaluating image formation either for design analysis or OPC adjustments. The objective of this paper is to analyze the influence of mask topography on imaging. The mask topography influences polarization state and diffraction efficiencies, which are determine further image formation. Therefore these parameters and their dependence on mask type, materials and pitches are of the major concern during the analyses. We analyze the process latitude and CD variations through pitch. The complete rigorous analysis shows improved process windows with the increase of feature aspect ratio and at the same time a large through pitch CD deviation compared to the conventional Kirchhoff diffraction model.