Two-dimensional strain mapping in semiconductors by nano-beam electron diffraction employing a delay-line detector

Abstract

A delay-line detector is established for electron detection in the field of scanning transmission electron microscopy (STEM) and applied to two-dimensional strain mapping in Si-based field effect transistors. We initially outline the functional principle of position-sensitive delay-line detection, based on highly accurate time measurements for electronic pulses travelling in meandering wires. In particular, the detector is a single-counting device essentially providing an infinite time stream of position-resolved events so that acquisition speed is not hindered by detector read-outs occurring in conventional charge-coupled devices. By scanning the STEM probe over stressor- and gate regions of a field effect transistor on a 100 × 100 raster, 10 000 diffraction patterns have been acquired within 3–6.5 min, depending on the scan speed. Evaluation of the 004 and 220 reflections yields lateral and vertical strain at a spatial resolution of 1.6 nm. Dose-dependent strain precisions of 1.2−1.8×10−3 could be achieved for frame times of 40 and 20 ms, respectively. Finally, the detector is characterised as to quantum efficiency and further scopes of application are outlined.

Mapping the full lattice strain tensor of a single dislocation by high angular resolution transmission Kikuchi diffraction (HR-TKD)

“…Thus far detailed characterisation of dislocations has mostly relied on TEM for determination of dislocation type, Burgers vector (b) and associated strain fields. The two most common methods for measuring lattice strain at the atomic scale are geometric phase algorithms (GPA) [27,28] and nano-beam diffraction in TEM [29][30][31]. Both offer a strain sensitivity of ~ and a spatial resolution of 2 to 3 nm [32].…”

Materials characterisation by angle-resolved scanning transmission electron microscopy

“…Although ultrafast cameras89101112131415 are currently introduced to the field of low-angle STEM, our approach exhibits several advantages. As quantitative analyses of atomically resolved STEM intensities rely on Voronoi diagrams16, Gaussian mixture models1718 or probe integrated cross sections19, each atomic column must be sampled with a sufficient number of probe positions.…”

“…Here, acquisition of the 2 K × 2 K data used for the measurement of composition, thickness and strain in GaNAs at atomic resolution took 5 min 40 s. Even with a pixelated, ultrafast detector operating at 2 kHz this recording would have taken 35 min and more than one hour at the more typical frame rate of 1 kHz. Moreover, we optimised the recordings such that intense low angle data are recorded faster than weak high angle data whereas direct detectors partially suffer from their limited dynamic range8914 or radiation hardness. Furthermore one is often interested in the signal integrated over a few dedicated angular intervals, so that the iris approach efficiently reduces the data to a manageable amount and overcomes the limited angular resolution and flexibility of multi-ring detectors2021 or strips of multiple apertures with fixed geometries22.…”

Atomic-scale quantification of charge densities in two-dimensional materials

“…This is now feasible as differential phase contrast [4][5][6] (DPC) STEM currently undergoes a rapid development from a classical, qualitative approach to quantitative electron picodiffraction [7,8] based on first moment detection [9]. The enhancement involves the acquisition of momentum-resolved STEM data, i.e., a 4D data set obtained by recording 2D diffraction patterns for a probe scanning a 2D raster, which requires current ultrafast cameras [10][11][12][13][14] being capable of submillisecond frame times.…”