SEM-Contour Based OPC Model Calibration through the Process Window
As design rules shrink, there is an unavoidable increase in the complexity of OPC/RET schemes required to enable design printability. These complex OPC/RET schemes have been facilitating unprecedented yield at k1 factors previously deemed ‘unmanufacturable,’ but they increase the mask complexity and production cost, and can introduce yield-detracting errors. This work compares two alternative methods for calibrating OPC models. The first method uses a traditional industry flow for making CD measurements on target structures at nominal process conditions, and the second uses 2D contour profiles extracted automatically by the CD-SEM over varying focus and exposure conditions. Model accuracy improvement using 2D contours for calibration through the process window is demonstrated. Additionally, this work addresses the issues of automating the contour extraction and calibration process, reducing the data collection burden with improved calibration cycle time.
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