A robust focusing and astigmatism correction method for the scanning electron microscope - Part III: An improved technique

Abstract

As described in a previous work, a new technique has been developed to perform automatic focusing and astigmatism correction on any general scanning electron microscope (SEM) sample ranging from gold-on-carbon to integrated circuit (IC) tracks. In this work, various improvements made to this technique are reported. They include the implementation of direct control of the SEM and the development of three new algorithms, namely the adaptive fast Fourier transform (FFT) algorithm, the coarse focusing algorithm, and the fine focusing algorithm. Direct control reduces the communication time with the SEM while the three new algorithms are integrated with the existing technique to make it even more robust to noise and to extend it to correct images with any degree of defocus and astigmatism. The enhanced focusing and astigmatism correction algorithm is able to perform the correction in a shorter time while maintaining the accuracy of the original algorithm even under noisy conditions.