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20 October 2006 Optical issues of thin organic pellicles in 45-nm and 32-nm immersion lithography
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The semiconductor industry will soon be putting >=1.07NA 193nm immersion lithography systems into production for the 45nm device node and in about three years will be putting >=1.30NA systems into production for the 32nm device node. For these very high NA systems, the maximum angle of light incident on a 4X reticle will reach ~16 degrees and ~20 degrees for the 45nm and 32nm nodes respectively. These angles can no longer be accurately approximated by an assumption of normal incidence. The optical diffraction and thin film effects of high incident angles on the wafer and on the photomask have been studied by many different authors. Extensive previous work has also investigated the impact of high angles upon hard (e.g., F-doped silica) thick (>700μm) pellicles for 157nm lithography, e.g.,. However, the interaction of these high incident angles with traditional thin (< 1μm) organic pellicles has not been widely discussed in the literature. In this paper we analyze the impact of traditional thin organic pellicles in the imaging plane for hyper-NA immersion lithography at the 45nm and 32nm nodes. The use of existing pellicles with hyper-NA imaging is shown to have a definite negative impact upon lithographic CD control and optical proximity correction (OPC) model accuracy. This is due to the traditional method of setting organic pellicle thickness to optimize normally incident light transmission intensity. Due to thin film interference effects with hyper-NA angles, this traditional pellicle optimization method will induce a loss of high spatial frequency (i.e., high transmitted angle) intensity which is similar in negative impact to a strong lens apodization effect. Therefore, using simulation we investigate different pellicle manufacturing options (e.g., multi-layer pellicle films) and OPC modeling options to reduce the high spatial frequency loss and its impact.
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Kevin Lucas, Joseph S. Gordon, Will Conley, Mazen Saied, Scott Warrick, Mike Pochkowski, Mark D. Smith, Craig West, Franklin Kalk, and Jan Pieter Kuijten "Optical issues of thin organic pellicles in 45-nm and 32-nm immersion lithography", Proc. SPIE 6349, Photomask Technology 2006, 63490K (20 October 2006);

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