Template Matching Approach for Automated Determination of Crystal Phase and Orientation of Grains in 4D-STEM Precession Electron Diffraction Data for Hafnium Zirconium Oxide Ferroelectric Thin Films.

Abstract

Thin film processing methods used to fabricate ferroelectric hafnium zirconium oxide typically result in small-grained films with a mixture of ferroelectric and nonferroelectric crystal phases with various crystallographic orientations. Although reliable, rapid determination of grain phase and orientation from four-dimensional scanning transmission electron microscopy maps is critical for measuring increased ferroelectric response, an assessment of automated analysis methods is not available. Here, a comparison of results between commercially available software (NanoMEGAS ASTAR) and an open-source code (py4DSTEM) is presented. Typically, the lamella used for STEM characterization are thicker than the average hafnium zirconium oxide (HZO) grain size, resulting in 4D maps where dynamical diffraction from more than one grain occurs in a significant number of pixels. Thus, precession electron diffraction (PED) data was required for reliable automated template matching analysis. Reliably distinguishing between the different crystal phases of HZO is challenging due to the small difference in lattice constant between phases and the possible presence of multiple orthorhombic phases. The HZO films in this study were characterized using PED, and precession diffraction simulation capability was added to py4DSTEM. Correlation of automated phase mapping with electrical verification of the ferroelectric effect confirmed the identification of the noncentrosymmetric space group 29 orthorhombic phase of HZO.