Contour-based self-aligning calibration of OPC models

SEM contours are used to complement CD measurements in OPC model calibration. This is done to capture 2D information about printed features into the model while CD measurement data is kept to maintain accuracy for 1D features. As the method progresses, there are emerging challenges that are normally not found in CD based calibration. One such challenge is the need to align SEM contours with calibration features. This is particularly important in determining model accuracy since contour calibration typically involves a cost function that compares the SEM contours to the simulated print images. This work explores a technique to include contour alignment errors into the calibration cost function. For each contour and its corresponding simulated print, the cost function returns an error value for a given set of model parameters. The error represents how well the model simulation compared to input contour. In addition, it also contains information on how far or how close the contour is aligned to simulation. Misalignment is to be eliminated on the fly during calibration and to be reported at the end of calibration. In this paper we describe the proposed technique and compare the results of calibration between aligned and misaligned contour data.