Nanoscale holographic interferometry for strain measurements in electronic devices

CEMES-CNRS, nMat Group, 29 rue Jeanne Marvig, 31055 Toulouse, France.
Nature (Impact Factor: 41.46). 07/2008; 453(7198):1086-9. DOI: 10.1038/nature07049
Source: PubMed


Strained silicon is now an integral feature of the latest generation of transistors and electronic devices because of the associated enhancement in carrier mobility. Strain is also expected to have an important role in future devices based on nanowires and in optoelectronic components. Different strategies have been used to engineer strain in devices, leading to complex strain distributions in two and three dimensions. Developing methods of strain measurement at the nanoscale has therefore been an important objective in recent years but has proved elusive in practice: none of the existing techniques combines the necessary spatial resolution, precision and field of view. For example, Raman spectroscopy or X-ray diffraction techniques can map strain at the micrometre scale, whereas transmission electron microscopy allows strain measurement at the nanometre scale but only over small sample areas. Here we present a technique capable of bridging this gap and measuring strain to high precision, with nanometre spatial resolution and for micrometre fields of view. Our method combines the advantages of moiré techniques with the flexibility of off-axis electron holography and is also applicable to relatively thick samples, thus reducing the influence of thin-film relaxation effects.

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Available from: E. Snoeck, Apr 03, 2014
    • "These points motivated us to carry out strain measurements of Nd–Fe–B sintered magnets using transmission electron microscopy (TEM). Strain measurements from thin-foil crystals have been carried out using several techniques of TEM, including geometric phase analysis (GPA) method [19] [20], convergent beam electron diffraction (CBED) [21] [22], nanobeam electron diffraction [23] [24], and dark-field electron holography [25] [26]. Although each of these methods has advantages and drawbacks, CBED achieves the highest precision of the order of 0.01% via the analysis of diffraction lines from higher-order Laue zones (HOLZ). "
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    ABSTRACT: Strain maps for Nd2Fe14B grains in Nd-Fe-B sintered magnets, representing elongation/contraction in the spacing of c planes, have been revealed by analyzing artificial moiré fringes in scanning transmission electron microscopy images. The strain maps were collected from several types of Nd2Fe14B grains in contact with metallic-Nd (m-Nd), Nd2O3, NdOx, and thin grain boundary phases. A maximum value of strain of ∼1.2% was observed at a Nd2Fe14B/m-Nd interface. The magnitude of strain for the interfaces with Nd2O3 and NdOx phases was 0.4-0.5%. The strain was negligible in the vicinity of the grain boundary phase. It appears that the observations are smaller than the theoretical values of strain that may cause a significant change in the magnetocrystalline anisotropy of the Nd2Fe14B phase.
    No preview · Article · Dec 2015 · Acta Materialia
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    • "Recently, Hytch et al. [10] invented dark-field electron holography , as an alternative method for measuring strain. The DFEH technique can provide 2-D strain measurement with a large field of view, high spatial resolution and high precision [7] [15] [16] [18]. "
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    ABSTRACT: In this paper, we carried out the two-dimensional (2D) strain measurement in sub-10 nm SiGe layer; images were obtained by dark-field electron holography (DFEH). This technique is based on transmission electron microscopy (TEM), in which dark-field holograms were obtained from a (400) diffraction spot. The measured results were compared to the X-ray diffraction (XRD) results in terms of the strain value and the depth of strain distribution in a very thin SiGe layer. Subsequently, we were able to successfully analyze the 2D strain maps along the [100] growth direction of the nanoscale SiGe region. The strain was measured and found to be in the range of 1.8–2.4%. The strain precision was estimated at 2.5 × 10−3. As a result, the DFEH technique is truly useful for measuring 2D strain maps in very thin SiGe layers with nanometer resolution and high precision.
    Full-text · Article · Sep 2015 · Current Applied Physics
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    • "Particularly, dark field electron holography in a TEM is also welladapted to measure strains over large fields of view with high spatial resolution [50]. Nevertheless, special hardware and operation mode are needed for performing this method. "
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    ABSTRACT: Revealing strains on the unit-cell level is essential for understanding the particular performance of materials. Large-scale strain variations with a unit-cell resolution are important for studying ferroelectric materials since the spontaneous polarizations of such materials are strongly coupled with strains. Aberration-corrected high-angle-annular-dark-field scanning transmission electron microscopy (AC-HAADF-STEM) is not so sensitive to the sample thickness and therefore thickness gradients. Consequently it is extremely useful for large-scale strain determination, which can be readily extracted by geometrical phase analysis (GPA). Such a combination has various advantages: it is straightforward, accurate on the unit-cell scale, relatively insensitive to crystal orientation and therefore helpful for large-scale. We take a tetragonal ferroelectric PbTiO3 film as an example in which large-scale strains are determined. Furthermore, based on the specific relationship between lattice rotation and spontaneous polarization (Ps) at 180° domain-walls, the Ps directions are identified, which makes the investigation of ferroelectric domain structures accurate and straightforward. This method is proposed to be suitable for investigating strain-related phenomena in other ferroelectric materials.
    Full-text · Article · Sep 2015 · Ultramicroscopy
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