Quantitative measurement of strain field in strained-channel-transistor arrays by scanning moiré fringe imaging

Jung

Applied Physics Letters

et al. 2014

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We report the use of scanning moiré fringe (SMF) imaging through high-angle annular dark-field scanning transmission electron microscopy (STEM) to measure the strain field around a CoSi2 contact embedded in the source and drain (S/D) region of a transistor. The atomic arrangement of the CoSi2/Si (111) interface was determined from the high-resolution (HR)-STEM images, and the strain field formed around the S/D region was revealed by nanometer-scale SMFs appearing in the STEM image. In addition, we showed that the strain field in the S/D region measured by SMF imaging agreed with results obtained via peak-pairs analysis of HR-STEM images.

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confidence: 99%

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confidence: 99%

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Direct observation of nanometer-scale strain field around CoSi2/Si interface using scanning moiré fringe imaging

Jung

Applied Physics Letters

et al. 2014

Self Cite

“…SMF imaging is a recently developed method that can measure strain fields at a high spatial resolution in the nanometer scale. [20][21][22] In the HAADF-STEM experiment, the SMFs appear when the scanning grating size d s is close to the crystal lattice spacing d l . Figure 1a shows the strained lattice spacing d l that increases from the bottom to the top of the pattern.…”

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confidence: 99%

“…We confirmed that the detector's inner angle of 45 mrad allowed us to obtain STEM image in HAADF regime. 21 The SMF images shown here were acquired at a magnification of 640 K with an acquisition time (dwell time) of 2 μs for each pixel. In order to obtain strain maps parallel to the strained channel, the translational SMFs formed by interfering scanning grating with the (220) lattice d-spacing of Si crystal were obtained and examined.…”

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confidence: 99%

Channel-Length-Dependence of Strain Field in Transistor Studied via Scanning Moire Fringe Imaging

ECS Solid State Letters

Lee

Oshima

et al. 2013

We have applied scanning moiré fringe (SMF) imaging to the quantitative measurement of the strain introduced in n-type channel transistors with embedded SiC in the source and drain. The tensile strain parallel to the channels was reveal with a nano-meter scale spatial resolution. We investigated the strain field in transistors with various channel lengths scaled down to 25 nm, and found that the strain increases up to 0.7% as the channel length shrinks to 35 nm. However, the strain in the channel decreases to 0. 55% as the channel length is scaled from 35 nm down to 25 nm. Strain engineering is routinely applied in the fabrication of advanced semiconductor devices to enhance the mobility of the carriers in transistors.1,2 The mobility of electrons or holes is boosted when the channel in a transistor is under either a tensile or compressive strain, respectively. The Si 1−x C x embedded in the source/drain region has been used for n-type field effect transistors.3 The lattice parameter of Si 1−x C x with a carbon concentration of about 1% is smaller than that of pure Si. Thus, a compressive stress is formed in the source/drain region, which in turn induces a tensile strain in the n-type channel. 4 Since the electrical performance of the device is greatly influenced by the strain field induced in the channel region, it is required to control the strain field for optimum manufacturing processing. Furthermore, with decrease in the size of modern semiconductor devices, the strain field in the semiconductor devices tends to be strongly influenced by layout design parameters such as the channel length and the geometry of the source and drain regions. 5,6 Therefore, for next-generation technology, it is required to monitor the layout-dependent strain behavior with high precision at nanometer-scale spatial resolutions. Although various tools have been applied to the measurement of strain fields in semiconductor structures, 4,7-17 there have been relatively few experimental results regarding studying the effect of the channel length on the strain field induced in semiconductor device structures. 18In this study, we have applied scanning moiré fringe (SMF) imaging, 19 which is a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM)-based technique, to quantitatively measure the strain field in transistors with various channel lengths down to 25 nm. SMF imaging is a recently developed method that can measure strain fields at a high spatial resolution in the nanometer scale. [20][21][22] In the HAADF-STEM experiment, the SMFs appear when the scanning grating size d s is close to the crystal lattice spacing d l . Figure 1a shows the strained lattice spacing d l that increases from the bottom to the top of the pattern. Figure 1b Fig. 1c. 22 Because the SMF spacing d SMF changes very sensitively to the variation in the lattice plane spacing d l , the strain field can be obtained by substituting the measured d SMF and a calibrated value of d s in the formula for the width of the translational moiré ...

European Microscopy Congress 2016: Proceedings

Mapping 2D strain components from STEM moiré fringes

Hÿtch

Gatel

Ishizuka

et al. 2016

Artificial moirés are created in a STEM by deliberately choosing a low magnification where the scan step is close to the crystalline periodicity (see Figure 1a) [1]. A moiré contrast then results from the interference between the scan and the crystal lattice. The technique has been developed to analyse strain [2], and has been applied to the study of strained‐silicon devices [3]. In reciprocal space, STEM moiré fringes can be understood as the convolution of the lattice created by the scan, characterized by the scan‐step, s in real‐space, or s * in reciprocal space, and the reciprocal lattice of the crystalline lattice, characterized by d * (Figure 1b). Interference between neighbouring periodicities gives rise to moiré fringes of periodicity q M . In general, only a few moiré fringe periodicities will be present in the image as the scan reciprocal lattice is in reality multiplied by the MTF of the probe: the size of the probe limits the possible interference terms (indicated by the yellow area in Figure 1b). The moiré peridocity q M is related vectorially to s * , which is usually 1 or 2 pixel −1 , and the d * (or g‐vector) for a particular set of lattice fringes (Figure 1c). Here we show how the strain information can be extracted using the concept of geometric phase, previously used for the analysis of high‐resolution TEM images [4]. The advantage of this formulation is that the moiré fringes do not need to be aligned exactly with the crystalline lattice, thus freeing up the experimental work. The periodicity of the moiré fringes (Figure 2a) is identified from the power spectrum of the image and the corresponding geometric phase determined (Figure 2b). The strain is in turn calculated from the geometric phase (Figure 2c). It is not necessary to know the exact calibration of the original image providing a reference region of known crystal parameter is present, as the vectorial relationship (Figure 1c) provides a strong constraint. We have also developed a procedure to determine maps of the 2D strain tensor from two differently oriented SMFs [5] (Figure 3). The results from two separate moiré fringe images need to be aligned (Figure 3b) and combined to determine the full 2D in‐plane strain tensor. Whilst the examples here are simulated, we anticipate presenting experimental results from devices and piezo‐electric materials.