Strain Measurement in Semiconductor Heterostructures by Scanning Transmission Electron Microscopy

Müller, Knut; Rosenauer, A.; Schowalter, Marco; Zweck, Josef; Fritz, R.; Volz, Kerstin

doi:10.1017/s1431927612001274

Cited by 63 publications

(64 citation statements)

References 31 publications

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“…Due to the incredibly large size of the datasets obtained, both in file size and number of disk positions to be measured, only the fastest algorithms are considered. For example, while other authors have used edge detection via Canny or Prewitt filters followed by circle fitting to find the center of the disk [8], that approach is very computationally intensive, requiring several iterative steps per disk in order to resolve a measurement with subpixel accuracy. Additionally, that method relies on accurate filter thresholds which can vary with the type of diffracted disk structure observed, decreasing general robustness and ease of use.…”

Section: Methods For Determining Diffraction Disk Positionsmentioning

confidence: 99%

“…Radial gradient maximization is another method used [21,8,22], in which concentric circles or ellipses are placed around an estimated disk center and their rotational averages are calculated. Since most disks have sharp edges, when the difference between the rotational average of concentric shapes are a maximum, the concentric shapes are properly placed around the center of the disk.…”

Section: Methods For Determining Diffraction Disk Positionsmentioning

confidence: 99%

“…Likewise in metallic specimens, understanding strain and its evolution under deformation will help further the understanding and predictive capabilities of the field. While many techniques of measuring strain exist [2,3,4,5,6,7,8,9], scanning convergent nanobeam electron diffraction (NBED) is attractive for a number of reasons. First, NBED strain mapping offers the potential of very high accuracy in strain measurement.…”

Section: Introductionmentioning

confidence: 99%

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Optimizing disk registration algorithms for nanobeam electron diffraction strain mapping

et al. 2017

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Scanning nanobeam electron diffraction strain mapping is a technique by which the positions of diffracted disks sampled at the nanoscale over a crystalline sample can be used to reconstruct a strain map over a large area. However, it is important that the disk positions are measured accurately, as their positions relative to a reference are directly used to calculate strain. In this study, we compare several correlation methods using both simulated and experimental data in order to directly probe susceptibility to measurement error due to non-uniform diffracted disk illumination structure. We found that prefiltering the diffraction patterns with a Sobel filter before performing cross correlation or performing a square-root magnitude weighted phase correlation returned the best results when inner disk structure was present. We have tested these methods both on simulated datasets, and experimental data from unstrained silicon as well as a twin grain boundary in 304 stainless steel.

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Section: Methods For Determining Diffraction Disk Positionsmentioning

confidence: 99%

Section: Methods For Determining Diffraction Disk Positionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Optimizing disk registration algorithms for nanobeam electron diffraction strain mapping

et al. 2017

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“…The spread in the local strain corresponds to around 0.3%. Taking into account that the precision of the nanodiffraction strain mapping technique is around 0.1%, 11 it can be concluded that this spread is considerably larger than the statistical error. The agreement of the mean local stress with the global stress demonstrates the applicability of the presented in situ strain mapping method and the ability to measure sample stresses without the need of a quantitative deformation holder and independent of the sample geometry.…”

mentioning

confidence: 98%

“…10 Alternatively, the precise measurement of diffracted peak positions allows for the determination of local strain in the material using Bragg's law. Nanodiffraction strain mapping is not only a very accurate technique 11 but also very robust; 12 while techniques based on high-resolution electron microscopy or electron holography have stringent sample requirements such as perfect zone-axis or the presence of an unstrained reference region in the field of view, nanodiffraction strain mapping is able to measure strain as long as the corresponding diffracted spots are visible and is therefore well suited for in situ deformation where some bending is inevitable. Nanodiffraction strain mapping is largely immune to dynamical scattering effects from large sample thicknesses because the measurement is only sensitive to the position of diffraction discs, not the details of fine intensity structure within the discs.…”

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confidence: 99%

Local and transient nanoscale strain mapping during in situ deformation

Gammer

Kacher

Czarnik³

et al. 2016

Applied Physics Letters

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The mobility of defects such as dislocations controls the mechanical properties of metals. This mobility is determined both by the characteristics of the defect and the material, as well as the local stress and strain applied to the defect. Therefore, the knowledge of the stress and strain during deformation at the scale of defects is important for understanding fundamental deformation mechanisms. Here, we demonstrate a method of measuring local stresses and strains during continuous in situ deformation with a resolution of a few nanometers using nanodiffraction strain mapping. Our results demonstrate how large multidimensional data sets captured with high speed electron detectors can be analyzed in multiple ways after an in situ TEM experiment, opening the door for true multimodal analysis from a single electron scattering experiment.

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Analysis of strain and composition in GeSi/Si heterostructures by electron microscopy

Müller‐Caspary

Oelsner

Potapov

et al. 2016

European Microscopy Congress 2016: Proceedings

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Electronic properties of GeSi/Si‐based metal oxide semiconductor field effect transistors (MOSFETs) are strongly influenced by the geometry, composition and strain state of the Ge containing source/drain stressor regions and the Gate channel in between. In the first part of our contribution, we hence present quantitative STEM Z‐contrast evaluations of the Ge composition in MOSFETs with different stressor geometries and verify the results with energy‐dispersive analyses of X‐rays (EDX) using the chemiSTEM system mounted on an FEI Titan facility. To evaluate the strain distribution within the gate channel and the stressors, we used nano‐beam electron diffraction employing a delay‐line detector (DLD, [1]) which enhances the acquisition speed for the 4‐dimensional data set (diffraction patterns as a function of the STEM raster position) to 10ms/image. As illustrated in Fig.1 the top of the DLD consists of a microchannel plate (MCP) stack that causes a cascade of secondary electrons for each 300keV electron impinging on the detector. The heart of the DLD are 2 meandering wires shown in blue and red in which each cascade causes electrical pulses travelling towards the ends of the wires. Depending on the incident position of the electron a characteristic time delay between the arrivals of the 2 conjunct pulses at the ends of a wire is measured with high accuracy, giving the coordinate of incidence perpendicular to the meander. By crossing two such delay‐lines the point (x,y) and time τ of incidence can be detected. Thus the DLD allows for both the recording of a continuous stream of single electron events processed by a time‐to‐digital converter (TDC) with a time precision in the picosecond range and the in‐situ integration of the signal over a certain frame time to obtain conventional images. Note that no pixel raster is involved here. The two modes of operation are illustrated in the right part of Fig. 1. An example for a MOSFET exhibiting 2 Ge regimes of 22% and 37% within the stressors is shown in Fig. 2 for the strain measurement along the [001] direction and in Fig. 3 for a measurement along the [110] direction. Here a STEM raster of 100x100 pixels was used with a dwell time of 40ms. Figure 2 was obtained by evaluating the position of the 004 CBED disc using the radial gradient maximisation method [2] whereas the 220 reflection was measured to obtain Fig.3. Two strain regimes are observed inside the GeSi stressors due to the different regimes of Ge contents. The gate channel exhibits compressive strain of up to 3% laterally and an expansion below 1% along [001]. Concerning the influence of the acquisition speed on strain precision, recording 10,000 diffraction patterns took 6.5min here, yielding a strain precision of 0.12% in terms of the standard deviation determined in unstrained Si regions. The same experiment at twice the scan speed (dwell time of 20ms) yields the same average strain distributions, however, at the precision of 0.18%. In the second part, we report a systematic study on the epitaxy of GeSi on Si (111) as a function of growth temperature. In particular, temperatures of 400, 450 and 550°C have been used and the strains along [111] and [1‐11] have been measured. Using elasticity theory, composition maps were derived from the strain results, yielding the three Ge profiles in Fig.4. Obviously growth at 400 and 450°C leads to islands of pure Ge whereas the Ge content drops to 60% if the temperature is raised to 550°C. We finally discuss our results with respect to Si/Ge interdiffusion which causes a gradual change of composition at the interface.

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Strain Measurement in Semiconductor Heterostructures by Scanning Transmission Electron Microscopy

Cited by 63 publications

References 31 publications

Optimizing disk registration algorithms for nanobeam electron diffraction strain mapping

Optimizing disk registration algorithms for nanobeam electron diffraction strain mapping

Local and transient nanoscale strain mapping during in situ deformation

Analysis of strain and composition in GeSi/Si heterostructures by electron microscopy

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