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17 May 1994 Fundamental analysis on fabrication of 256-MB DRAM using phase-shift mask technology
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This paper describes the phase shift mask (PSM) effects in view of production using i-line lithography. For the PSM technology, it was hard to control process because the process condition was limited by the exposure tool. To fabricate the 256MB DRAM with 0.25 micrometers minimum feature size (MFS), we evaluated the PSM including attenuated type for conventional patterns and a 0.25 micrometers cell array using positive and negative tone phase shift mask for actual process. Furthermore, we applied various approaches to get a sufficient depth of focus (DOF) and high resolution using an i-line system with 0.57 NA, an off-axis illumination system, low partial coherence factor, and process in cases of alternating, subresolution, and attenuated type of phase shift mask. As a result, even if pattern delineation was possible, we should optimize design, topology structure, and process to get enough DOF margin, good uniformity, and high repeatability for device fabrication.
© (1994) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Young-Mog Ham, YoungSik Kim, Ikboum Hur, Ki-Yeop Park, Hung-Eil Kim, Dong-Jun Ahn, and Soo-Han Choi "Fundamental analysis on fabrication of 256-MB DRAM using phase-shift mask technology", Proc. SPIE 2197, Optical/Laser Microlithography VII, (17 May 1994); doi: 10.1117/12.175419;

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