The world's first electron projection lithography (EPL) R&D exposure tool was installed at our laboratory in June 2003, and we have evaluated its basic performance. The most feasible introduction of EPL into ultra-large-scale integration (ULSI) is mix-and-match use with an optical tool for critical layers at the 65 nm technology node (TN) and beyond. Overlay is the most crucial issue in mix-and-match lithography, so we focused on overlay in this evaluation. We found that the overlay performance of the EPL tool in mix-and-match use is 48.0 nm in the X direction and 45.7nm in the Y direction. To clarify details of deteriorated overlay accuracy, we divided it into 7 factors, finding underlayer distortion to be about 15 nm, residual reticle distortion 5 nm, subfield (SF) distortion 15 nm, main-field (MF) distortion 20 nm, reticle alignment accuracy 15 nm, repeatability 25 nm, and exposure field distortion 25 nm. We also demonstrated that overlay accuracy was 30 nm using previous overlay data.
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