Alternatives to Alternating Phase Shift Masks for 65nm
193nm lithography is very likely to be the pattern transfer method of choice for 65nm technology. This means lithography with a k1 factor in the range of 0.3, so strong resolution enhancement techniques (RET) are necessary. Until recently, alternating Phase Shift Masks (alt.PSM) seemed to be the only viable option. Rather stringent layout restrictions, complex mask manufacturing, and the throughput loss due to the required double exposure make this option rather costly. Double exposure of chromium masks or halftone (embedded) PSM with dipole illumination (DDL), or single exposure of chrome-less PSM (CPL) are evaluated as alternatives with proven resolution for the minimum feature size. Both techniques need sub-resolution features to compensate for their sub-optimum performance on either isolated lines or on lines of about twice the minimum width (in case of CPL). To linearize such highly non-linear pattern transfer processes, model-based Optical Proximity effect Correction (OPC) is mandatory for both options.
This paper demonstrates the automated generation of the basic mask writing data for both DDL and CPL for arbitrary layouts, followed by model-based OPC, using Calibre for both steps. Sufficient pattern fidelity and pattern robustness (over a 300nm defocus range) has been shown for a gate/polysilicon layer of a 65nm layout. The results were obtained using masks with reasonable mask specifications.
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