Improved measurement accuracy in optical scatterometry using fitting error interpolation based library search

Abstract

Library search is one of the most commonly used methods for solving the inverse problem in current optical scatterometry. One issue in the conventional library search method is that its final measurement accuracy is fundamentally limited by the grid interval of each parameter in the signature library. In this paper, we propose a fitting error interpolation based library search (FEI-LS) method to improve the measurement accuracy. By comparing the interpolated fitting errors estimated in a FEI-based fine search step, the structural parameters associated with the minimum interpolated fitting error can be treated as the final measurement result. Experiments performed on a photoresist grating have demonstrated that the FEI-LS method can achieve a higher measurement accuracy for a pre-generated library without remarkable influence on the search speed. It is expected that the FEI-LS method will provide a useful and practical means for solving the inverse problem in the state-of-the-art optical scatterometry.