3D reconstruction of 3D NAND memory etch profiles using FIB-SEM: identifying variances in etched hole patterns

The semiconductor industry plays a pivotal role in advancing various global technology sectors, such as data processing and artificial intelligence, which drive the need for ongoing innovation. As memory and logic technologies progress, they yield increasingly complex and powerful chips. Unlike 2D NAND technology, which relies on lithographic patterning for scaling and yield, 3D NAND technology requires precise control over deposition and etch processes. Specifically, etching high aspect ratio (HAR) features in 3D NAND presents substantial challenges, particularly during the etching of memory holes, which inspires innovations like cryogenic etch processes. While these processes can improve throughput and reduce costs, they also introduce issues such as inner/outer hole loading, twisting, bowing, and incomplete or partial etching of holes. Addressing these challenges requires reliable monitoring and adjustment of the etch process to enhance reliability and yield. This paper presents a detailed study using focused ion beam-scanning electron microscopy (FIB-SEM) to analyze 3D NAND channel hole etching. We investigate the effects of patterning density on critical dimensions (CD), CD profile, CD ellipticity, kink, twisting and distortion, as well as etch depth variance at pattern edges and within the pattern. By leveraging 3D reconstruction modeling, which provides the capability to visualize and analyze individual channels in three dimensions and make virtual slices in any direction, this study aims to identify variances, reveal defects, and to ultimately, optimize the etching process.