HAADF-STEM block-scanning strategy for local measurement of strain at the nanoscale

TL;DR

This paper introduces a novel block-scanning strategy for high-resolution STEM imaging that reduces artifacts and extends the field of view, enabling accurate local strain measurement at the nanoscale without specialized diffraction equipment.

Contribution

A new scanning method that minimizes distortions and allows flexible resolution tuning, improving local strain measurement in nanoscale semiconductor devices.

Findings

Reduces scanning artifacts and drift effects.

Enables flexible spatial resolution and larger field of view.

Achieves strain measurement accuracy comparable to diffraction techniques.

Abstract

Lattice strain measurement of nanoscale semiconductor devices is crucial for the semiconductor industry as strain substantially improves the electrical performance of transistors. High resolution scanning transmission electron microscopy (HR-STEM) imaging is an excellent tool that provides spatial resolution at the atomic scale and strain information by applying Geometric Phase Analysis or image fitting procedures. However, HR-STEM images regularly suffer from scanning distortions and sample drift during image acquisition. In this paper, we propose a new scanning strategy that drastically reduces artefacts due to drift and scanning distortion, along with extending the field of view. The method allows flexible tuning of the spatial resolution and decouples the choice of field of view from the need for local atomic resolution. It consists of the acquisition of a series of independent small subimages containing an atomic resolution image of the local lattice. All subimages are then analysed individually for strain by fitting a nonlinear model to the lattice images. The obtained experimental strain maps are quantitatively benchmarked against the Bessel diffraction technique. We demonstrate that the proposed scanning strategy approaches the performance of the diffraction technique while having the advantage that it does not require specialized diffraction cameras.