Abstract
Resolution-enhancement technologies such as phase-shifting masks (PSMs) and modified illumination are currently critical issues in optical lithography. Because the most effective way to obtain higher resolution is by using PSM technology, we have examined light intensity profiles for various types of PSMs by simulation and found that the PSM structure with an SOG phase-shifter on a thin Cr layer is one of the best choices for KrF excimer laser lithography. We also examined potential problems, such as the durability of SOG materials and phase angle error due to surface topography of the Cr patterns, and found not only that no significant degradation occurs when the SOG phase-shifter is exposed to KrF excimer laser light, but also that the phase angle can be controlled precisely enough for gigabit-level ULSI device fabrication. We used improved 0.16 micrometers design rule PSMs to successfully delineate, with sufficient DOF range, several layers of experimental 1-Gb DRAM devices.
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