29 June 1998 Enhanced microlithography using coated objectives and image duplication
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Abstract
Two processes were investigated theoretically using both a scalar wave optics model and a microlithography simulation tool (Solid-C). The first method introduces a phase- transmission filter into the exit pupil plane. The results of both the scalar optics calculation (aerial image) and the Solid-C simulation (resist image) show that the final image profile is optimum, when the exit pupil plane filter is divided into two zones with the inner zone having a phase retardation of (pi) rad with respect to the outer one and the ratio of the radii of the zones is 0.3. Using this optimized filter for the fabrication of isolated contact holes, the focus-exposure process window increases significantly, and the depth of focus (DOF) can be enhanced by a factor of 1.5 to 2. The second technique enhances the DOF of the aerial image by means of a birefringent plate inserted between the projection lens and the wafer. As the shift in focus introduced by the plate strongly depends on the refractive index, two focal points will appear when using a birefringent plate instead of an isotropic plate: the first one is created by the ordinary, and the second one is created by the extraordinary ray. The distance between these images can be controlled by the thickness of the plate. The results of the calculations show that application of a thin but strongly birefringent material is a better candidate than using a slightly birefringent but thick plate, since aberrations proportional to the thickness can cause undesirable effects.
© (1998) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Miklos Erdelyi, Zsolt Bor, Gabor Szabo, Frank K. Tittel, "Enhanced microlithography using coated objectives and image duplication", Proc. SPIE 3334, Optical Microlithography XI, (29 June 1998); doi: 10.1117/12.310787; https://doi.org/10.1117/12.310787
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