We investigate on how to improve the performance of thickness determination from the optical scatterometry spectrum using machine learning. Our investigation is focused on a specific application for thick layered structures for 3D NAND with oxide/nitride repeating pairs. Since fast determination of thickness of every layer or detection of any outlier is not very efficient with the regression analysis using an optical model-based calculation due to requirement of a huge amount of calculations along with many parameters, machine learning (ML) can be applied for this application pursuing a faster solution. However, we also need to achieve its precision and accuracy as good as possible under a limited amount of ML train data sets. In order to carry out an efficient extraction or selection of features from data which is very important for improved performance of ML, we applied Fourier analysis of spectrum and investigate on how ML performance is improved.
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