A diffraction-based overlay model based on FDTD method

Abstract

As well known that, the critical dimension continues to shrink and the overlay control appears to become much more challenging than before. In such situation, we are seeking for solutions to minimize the impact of measurement shift in overlay detection induced by process variations. When the accuracy of overlay measurement improved, corrections can be performed effectively according to the feedbacks from metrology results. We build a physical model for simulating overlay metrology employing diffraction based overlay (DBO) principles, which can help to conduct researches on DBO metrology in advanced semiconductor nodes. In this paper, we present a physical model of the DBO metrology which based on the Finite-Difference Time-Domain (FDTD) method. The basis and principles of model establishment was discussed. After adjusting the model parameters compatible with the actual measurement conditions, the metrology wavelengths which provide the best accuracy and robustness of DBO measurement can be selected through simulations. The results of our study will be demonstrated in this publication.