Highly accurate model-based verification using SEM image calibration method

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In the past when design rule is not tight, CD-based OPC modeling was acceptable. But shrinkage of design rule eventually led to small process window, which in part increased MEEF(Mask Error Enhancement Factor). Hence, data for OPC modeling have also become more complex and diverse in order to characterize the critical OPC models. The number of measurement points for OPC model evaluation has increased to several hundred points per layer, and metrology requests for realizing pattern shapes on the wafer are no longer simple one-dimensional measurements. Traditional CD-based OPC modeling is based on 1 dimensional parameter fitting and has limited information. Due to this reason, the accuracy of the model has intrinsic limitations. Recently, development of modeling methodology resulted in SEM image calibration. SEM image calibration use SEM image to calibrate large volume 2 dimensional information. SEM image calibration is based on real SEM image which has several thousands of CD information. It needs only SEM images instead of several hundred CD data, so data feedback is more easy. But this approach makes it difficult to achieve confidential level for predictability because SEM image is restricted to local region. And modeling accuracy is highly dependent on SEM image quality and local position. In this paper, we propose SEM image calibration method that feeds back SEM image calibrated model to model-based verification. By using this method, modeling accuracy is increased and better post OPC verification can be made. We will discuss the application result on sub-60nm device and the feasibility of this approach.