ELECTROMAGNETIC STUDY OF A PHOTOLITHOGRAPHY SETUP FOR PERIODIC MASKS AND APPLICATION TO NONPERIODIC MASKS

We develop a rigorous electromagnetic analysis to study the field diff racted by a metallic or dielectric grating made of rectangular rods, l ying over a stratified media. The analysis generalizes the modal theor y of perfectly conducting lamellar gratings combined with the R-matrix propagation algorithm in order to avoid numerical instabilities, thus allowing treatment of layers and gratings of arbitrary thickness. We then study the field map obtained under the conditions stated in a pre vious patent that described a process for casting on a support the fai thful reproduction of a mask pierced with periodically distributed sli ts. We make a systematic study of the influence of the various paramet ers (incidence, mark-space ratio, groove spacing, groove depth, polari zation, conductivity of the metal) on the field map below the mask. We discover a large tolerance over the parameters, close to the values s tated in the patent. The result is that the setup described in the pat ent valid for periodic maps can be used for duplicating nonperiodic ma sks (e.g., linear Fresnel zone plates) as well as chirped gratings or gratings with nonrectilinear grooves. (C) 1996 Optical Society of Amer ica