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Investigation on accuracy of process overlay measurement

The shrinkage of design rule necessitated corresponding tighter overlay control. However, in advanced applications, the extension of current technology may not be able to meet the control requirement, consequently, additional breakthroughs are required. In this study, we investigated methods to enhance the overlay control, approaches by extraction of real overlay error out of overlay measurement. So far, only the destructive inspections like vertical SEM have enabled us to measure real misalignment. But, a concept of non-destructive method is proposed in this paper, extracting vertical information from the results of multiple measurements with various measurement conditions, keys or recipes. With this proposed method, the measurement accuracy can be improved and we can enable a new knob for overlay control.