Name: comprehensive characterization of extended defects in semiconductor materials by a scanning electron microscope
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Description: Watch this Scientific Journal Video about Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope at JoVE.com

Support of this work by the German Research Foundation (DFG) within the framework of the Research Training Group 1621 is gratefully acknowledged by Paul Chekhonin. All authors are grateful to Dietmar Temmler (Fraunhofer FEP Dresden) for providing the electron beam processed Si samples showing liquid phase re-crystallisation. Special thanks go to Stefan Saager and Jakob Holfeld for the preparation of the figures for the SEM equipment and the EBSD set-up. We thank Michael Stavola for detailed discussions and help with this work.

<ol>
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The authors have nothing to disclose.

The SEM offers the possibility to locate extended defects in the semiconductor material as well as to characterize their structural, optical and electrical properties by the application of ccEBSD, CL and EBIC investigations. In general, it is not possible to perform all three methods simultaneously on the same sample. However, a combination of results obtained by the different complementary investigation methods, when performed in a reasonable sequence, leads to a deeper understanding of the physical nature of the effects caused by extended defects.
For the CL measurements giving information on the optical properties of extended defects, a critical step in the protocol is the sample positioning procedure (step 1.6) due to undesired annealing of defects in the sample during the heating of the indium foil (which ensures a good thermal and electrical contact of the sample with the sample holder). An alternative to the procedure proposed is to mount the sample onto the sample holder by conductive silver paste at RT. However, from experience it is known that the organic solvent in the paste can cause carbon contamination on the sample surface during the scan in the SEM. The contamination degrades the quality of the CL images as well as of the EBSD diffraction patterns. Additionally, the step 4.21 requires special attention, where an abrupt rise of the luminescence intensity of silicon can occur during the cooling-down of the sample. This can harm the performance of the photomultiplier. On the contrary, for the case of unexpected low luminescence intensity for the actual sample, one should try to improve the adjustment of the light-collecting mirror (protocol No. 4.23) because the preliminary mirror alignment was performed on a test sample at RT in a slightly different range of wavelength.
Concerning instrumental limitations of the method, one has to take into account that at very low temperatures the stage with the sample can be moved only by &#177; 5 mm in the x- and y-directions which restricts the area of the samples under investigation. This limitation is due to the danger of brittle fracture of the He transfer tube. The sample dimensions for cryo-experiments given in 1.1 and 1.2 are also limited by experimental conditions. So the surface area of the samples should be adjusted to the size of the sample holder to ensure an optimal thermal contact on the heat sink. The low recommended thickness of the silicon samples limits the temperature gradient in the sample for the cryo-experiments. For a sample thickness of 200 &#181;m, the temperature in the center of the interaction volume for the primary electrons in the surface region was found to be increased by less than 5 K in comparison to the temperature measured at the surface of the sample holder. The high scan speed and the low magnification proposed only for the cool-down procedure in steps 4.5 and 4.17, ensure that the region of interest is kept clean. This is because of the heat transfer by the scanning electron beam which maintains a temperature always slightly above the temperature of the rest of the sample regions which act as condensation trap for residual gas in the SEM chamber. Generally, all the parameters listed in step 4.24 for CL spectroscopy are optimized for the measurement of the so called D line luminescence in bulk silicon by the experimental set up according to the equipment list. The parameters have to be adapted if investigations of the luminescence are to be carried out on other semiconductor materials.
Independent of the energy range of the luminescence observed, a further limitation of the CL measurements results from the light-collecting mirror because light coming from radiative recombination processes in the whole recombination volume is collected by the mirror and thus determines the grey value of the corresponding CL image pixel which is assigned to the position of the electron beam on the sample surface. Because the diameter of the recombination volume (which is comparable to the excitation volume) is larger than the pixel size even at low magnification, this effect causes a spatial smearing of the luminescence signal, and, therefore, limits the spatial resolution. Nevertheless, the CL investigation enables an imaging of the local distribution of mono- or panchromatic luminescence with a medium spectral resolution and could be combined with photoluminescence investigations to give a higher spectral resolution. Recently, as an alternative experimental method to CL measurements, a microscopic and spectroscopic mapping of dislocation related photoluminescence was proposed by the group of Tajima and co-workers26. The spatial resolution of the photoluminescence mapping is clearly lower than in CL images, but the photoluminescence investigations additionally allows the polarization of the deep level emission band correlated to dislocations to be determined in LAGBs with twist and tilt structures27,28.
In the case of EBIC investigations, which give insight into the electrical properties of extended defects, there are no alternative methods for the imaging of the locally varying charge-collection efficiency in semiconductor materials with a comparably spatial resolution. However, also for EBIC measurements, critical steps are included in the protocol. So in step 5.13, the variation of the EBIC image with decreasing temperature is expected to arise from the temperature dependent properties of the extended defects. However, the quality of the contacts can change at temperatures below RT and hence influence the EBIC image. Temperature affects the Schottky contact, made with an appropriate layer of Al in the case of p-type and with Au in the case of n-type silicon, because of the different coefficients of thermal expansion separating the contact layer from the silicon substrate. Furthermore, the ohmic contact made by a gallium-indium eutectic is not stable at temperatures below 160 K. Normally, the reduction of the contact quality leads to a strongly decreased EBIC signal for large areas. In this case, the contacts have to be renewed. For EBIC investigations at RT, it is also conceivable that the contacts for the EBSD measurements can be made by bonding the sample to an appropriate carrier board. Another instrumental limitation of EBIC measurements is caused by the protruding of the contact tip holders above the sample surface. To prevent a collision between the contact tip holder and the pole piece of the SEM the WD should be at least 15 mm.
In the experimental procedure for ccEBSD investigations which can be used to estimate the long-range strain field of extended defects, the following steps are critical. The most challenging part of the experiment is the sample preparation, especially the last polishing procedure (protocol No. 3.1) which has to be performed carefully to avoid the generation of additional surface defects. If no Kikuchi pattern can be obtained, often the quality of the sample surface is not sufficient. However, from silicon single crystals with slip lines on the surface after plastic deformation, a good diffraction pattern could be obtained which was well suited for the ccEBSD evaluation procedure. The surface roughness of these samples was analyzed by atomic force microscopy yielding a height variation in the range of up to 500 nm. Therefore, extremely high internal strains or amorphous surface layers seem to be responsible for blurred diffraction patterns rather than the imperfect smoothness of the sample surface. A further issue could be a low signal from the coherently scattered electrons in comparison to the background. Then an increase of the probe current at constant acceleration voltage and/or a more accurate determination of the background signal (protocol step No. 6.12) are helpful. To minimize sample movement during a long-lasting ccEBSD measurement it is recommended to fix the sample mechanically (protocol No. 3.2).
Instrumental limitations for the ccEBSD investigations can arise if the tilt of the sample surface relative to the incident electron beam is realized by the tilt of the stage. There are then strong restrictions for the movement of the sample due to a collision risk with the pole piece and the chamber walls. Furthermore, it is strongly recommended to use only line scans that are parallel to the tilt axis (and thus appear horizontally on the SEM screen), because, first, vertical scans have a large sum error for the internal strains due to the error of sample tilt. Second, during EBSD, the lateral resolution is higher (factor of about 3 for 70&#176; tilt) along the tilt axis than perpendicular to it. The lower limit for the value of the strain tensor components calculated for Si from ccEBSD investigations is about 2 x 10-4 which is the random error. Additionally it must be emphasized that the ccEBSD technique cannot be applied in the presence of large lattice rotations (&#62;4&#176;) referring to the reference point or very close to grain boundaries, where EBSD patterns from different grains overlap. The physical limitation of the ccEBSD investigations concerning the spatial resolution of the strain determination is due to the range of the electron diffraction which was found to be approximately 50 nm along the sample tilt axis. In comparison with X-ray diffraction experiments for the determination of internal strains, this is a clear advantage because of the significantly larger interaction volume of X-rays even in the case of X-ray &#181;-diffraction. For semiconductor materials, the investigation of perturbations of the isotropic refractive index by a polarscope can also be applied for the determination of internal stresses, but the spatial resolution of this method is lower than some hundred nm29. An alternative method for the determination of the spatially resolved three-dimensional strain state in crystals is based on the splitting of higher order Laue zones (HOLZ) lines. This method has to be performed in a transmission electron microscope (TEM) using an electron biprism for electron interferometry30. However, in contrast to the ccEBSD investigations in the SEM, the TEM investigation requires the preparation of a foil from the sample that changes the internal strains due to relaxation effects.
In future studies, ccEBSD measurements will also be performed at low temperatures. This will allow the investigation the structural, optical and electrical properties, not only on the same extended defect, but also at the same temperature.

It has been known for decades that extended defects exert an influence on the electronic structure of semiconductor materials1-3. The effect of extended defects on the performance of electronic devices and other applications such as sensors and solar-cell materials is under extensive experimental and theoretical investigation. Nevertheless, there is no generally accepted theory for the calculation of the electronic states of semiconductors in the presence of extended defects. This is due to the complexity of electronic structure calculations in the case of deviations from the ideal crystal lattice and also to the large diversity regarding the types and configuration of extended defects, as well as the possible combinations among them and with 0-dim intrinsic and extrinsic defects.
The main types of extended defects are dislocations (1-dimensional defects) and grain boundaries (2-dimensional defects). In the following, we concentrate on both of these types of extended defects in terms of the experiments that can be performed in the scanning electron microscope (SEM). The experimental methods presented here give information about structural, optical and electrical properties of extended defects and, therefore, indirect knowledge of the electronic states in semiconductor materials containing extended defects. The control of the defect-related electronic states is a central issue for the application of semiconductors and the operation of semiconductor devices.
For the structural investigation of extended defects, the electron backscatter diffraction (EBSD) technique can be applied. Usually, an EBSD measurement is performed by point mapping with a stationary electron beam at each point. EBSD then yields information about the crystallographic orientation of the crystal lattice of the sample in the case of single-crystalline material and of the grains in polycrystalline materials. For that purpose the experimentally determined diffraction patterns formed by the Kikuchi bands have to be analyzed by comparison with simulated patterns determined from the crystal space group of the material. If the software for the evaluation of the orientation data is able to calculate the misorientation angle between the crystallographic coordinate systems of neighboring mapping points, the type of grain boundary between them can be determined. If the misorientation angle is smaller than 15&#176;, a low angle grain boundary (LAGB) is present; otherwise it is a high angle grain boundary (HAGB). The type of HAGB is characterized by its&#160;&#931; value where &#931;-1 is the fraction of lattice points lying on a coincidence lattice. So, &#931; = 3 stands for the highly symmetric twin boundary4. If the EBSD mapping on two planes of the sample surface can be measured with an accurate knowledge of the positions of the mappings, the type of the grain boundary plane with Miller indices hkl can also be evaluated by a method proposed by Randle5.
Recently, a new procedure for the evaluation of the electron diffraction pattern was derived by Wilkinson et al.6 which allows the calculation of all components of the complete local strain tensor, i.e., absolute values of the three normal strain and the three shear strain components. This calculation is performed for each measuring point in a mapping from the corresponding diffraction pattern with respect to a reference pattern taken on an unstrained crystal region with the same crystallographic orientation. This evaluation procedure is based on the determination of small shifts of characteristic features of the EBSD pattern using the cross-correlation technique which gives the name ccEBSD. Relative to a chosen reference point, the strain components and lattice rotations can be measured with precisions of 10-4 and 0.006&#176;, respectively7. Applying ccEBSD measurements in line scans across grain boundaries, or along arrangements of dislocations, one can determine locally the amount as well as the range of the strain fields of these extended defects.
The optical properties of dislocations and grain boundaries can be investigated by spectral and imaging cathodoluminescence (CL) techniques. The luminescence signal is caused by the radiative recombination of electron-hole pairs which are generated in the semiconductor material by the primary electron beam of the SEM. The intensity of the luminescence is proportional to the radiative recombination efficiency which is the ratio of the total minority carrier life time to the radiative recombination time. When this ratio is influenced locally by defects, a contrast in the luminescence distribution can be observed in the CL images. Normally, extended defects act as non-radiative recombination centers and, therefore, the luminescence from band-band-recombination is decreased in the vicinity of extended defects in comparison to the undisturbed semiconductor. However, in the case of Si, Ge and some compound semiconductor materials, at dislocations as well as on grain boundaries, characteristic luminescence bands are observed showing photon energies lower than that of the (direct or non-direct) band-to-band recombination in the bulk material8-10. As an example, extensive CL investigations of bonded silicon wafers and of multi-crystalline silicon by Sekiguchi and co-workers11-13 revealed that dislocations and LAGBs are responsible for the occurrence of shallow and deep levels in the band gap. The corresponding radiative transitions are denoted as D lines in the CL spectra. Nevertheless, the role of the strain field accompanying arrangements of dislocations and of dislocation contamination by oxygen precipitation and transition metal impurities is still controversial for the interpretation of the D line luminescence. But, if an assignment of the energy position of the luminescence line to a distinct extended defect can be successfully made, then the occurrence of this specific line in the luminescence spectrum can be taken as a signal for the presence of this defect. To increase the luminescence intensity, i.e., the radiative recombination in relation to the non-radiative one, CL investigations have to be performed at low temperatures (cryo-CL) for semiconductor materials with indirect band structures.
The electrical properties of the extended defects considered here are characterized by imaging the electron beam induced current (EBIC) in the SEM. This current can be observed when electron-hole pairs generated by the primary electron beam are separated by a built-in electric field. This field can be generated by the electric potential of the extended defects themselves or by Schottky contacts on the sample surface. The EBIC image contrast results from local variations of the charge-collection efficiency due to a varying recombination behavior at electrically active defects. The extended defects usually show an increased carrier recombination so that they appear darker in an EBIC image than defect free regions. In the framework of physically based models of defects14, a quantitative evaluation of the spatial dependence of the EBIC signal, which is called contrast profile, enables the determination of the minority carrier diffusion length and lifetime as well as the surface recombination velocity. Because these parameters are dependent on temperature, EBIC investigations should also be performed at low temperature (cryo-EBIC) to obtain an enhanced signal to noise ratio. Alternatively, temperature dependent EBIC measurements enable the determination of the concentration of deep level impurities at dislocations according to a model which was proposed by Kittler and co-workers15,16.
It should be noted that the optical and electrical properties of extended defects in semiconductors can be influenced significantly by contamination and by 0-dim intrinsic defects17 which cannot be resolved by scanning electron microscopy. However, the combination of the experimental methods, ccEBSD, CL and EBIC, offers the chance to visualize the extended defects and to quantify their fundamental properties in the SEM. For future applications, where not only failure analysis, but also defect control and defect engineering are intended, this powerful tool will play an important role in the improvement of the performance of semiconductor devices.

<table><tbody><tr><td>Cryogenic liquids:&amp;nbsp;&amp;nbsp;&amp;nbsp;</td><td>Linde http://www.linde-gas.de, Air Liquide http://www.airliquide.de/</td><td></td><td></td></tr><tr><td>Liquid helium ( LHe )</td><td></td><td></td><td>for cooling of the cryostat</td></tr><tr><td>Liquid nitrogen ( LN2 )</td><td></td><td></td><td>for cooling of the PMT R5509-73</td></tr><tr><td>Indium wire</td><td>chemPUR http://chempur.de/&amp;nbsp;</td><td>900898</td><td>CL sample preparation: for good electrical and thermal coupling between cryostat and sample</td></tr><tr><td>Mica</td><td>plano GmbH http://www.plano-em.de/&amp;nbsp;</td><td>V3</td><td>isolation of EBIC sample holder and good thermal coupling to the cryostat</td></tr><tr><td>Aluminium wire, gold wire</td><td>chemPUR http://chempur.de/&amp;nbsp;</td><td>009013, 900891</td><td>purity 99.99%, material for formation of Schottky contact for EBIC measurements</td></tr><tr><td>Indium-Gallium eutectic solution</td><td>Alfa Aesar&amp;nbsp;</td><td>12478</td><td>to form ohmic contact on the backside of the sample for EBIC measurements</td></tr><tr><td>Liquid chemicalsVLSI Selectipur&lt;br/&gt; &amp;nbsp;(de-ionized water, acetone, ethanol)</td><td>VWR</td><td>52182674,&lt;br/&gt; 51152090</td><td>for sample preparation: cleaning and surface treatment</td></tr><tr><td>Hydrofluoric acid</td><td>VWR</td><td>1,003,382,500</td><td>necessary to remove surface oxide layer on Silicon samples immediately before investigation; follow safety precautions!&amp;nbsp;</td></tr><tr><td>MicroCloth</td><td>Buehler http://www.buehler.com/&amp;nbsp;</td><td>40-7222</td><td>polishing cloth</td></tr><tr><td>MasterMet 1 (0.02 &amp;micro;m)</td><td>Buehler http://www.buehler.com/&amp;nbsp;</td><td>40-6380-006</td><td>SiO&lt;sub&gt;2&lt;/sub&gt; polishing suspension</td></tr><tr><td>Scanning electron microscope (SEM)</td><td>Carl Zeiss AG http://www.zeiss.de/microscopy/&amp;nbsp;</td><td>Ultra 55</td><td>field emission gun</td></tr><tr><td>SEM-CL system</td><td>EMSystems</td><td></td><td>customized, following equipment belongs to CL system:</td></tr><tr><td>&amp;nbsp;SEM stage for cryostat</td><td>Kammrath &amp;amp; Weiss http://www.kammrath-weiss.com&amp;nbsp;</td><td></td><td></td></tr><tr><td>KONTI cryostat</td><td>Cryovac http://www.cryovac.de/</td><td>3-06-4609C-7674</td><td>cooling of sample</td></tr><tr><td>Liquid He transfer line for KONTI cryostat</td><td>Cryovac http://www.cryovac.de/</td><td>3-01-3506C-SO</td><td></td></tr><tr><td>Cryogenic Temperature Controller</td><td>Cryovac http://www.cryovac.de/</td><td>TIC-304 MA</td><td>controlling the flow rate of cryogenic</td></tr><tr><td>Photomultiplier Tube (PMT)&amp;nbsp;</td><td>Hamamatsu http://www.hamamatsu.com</td><td>R5509-73</td><td>for NIR spectral range&amp;nbsp;</td></tr><tr><td>PMT housing and cooler</td><td>Hamamatsu http://www.hamamatsu.com</td><td>C9940-2</td><td></td></tr><tr><td>HV power supply&amp;nbsp;</td><td>Heinzinger electronic GmbH http://www.heinzinger.de/</td><td>LNC 3000-10 neg</td><td>for operating of the PMT</td></tr><tr><td>Monochromator&amp;nbsp;</td><td>Sol Instruments Ltd. http://www.solinstruments.com</td><td>MS2004i</td><td></td></tr><tr><td>PMT&amp;nbsp;</td><td>Hamamatsu http://www.hamamatsu.com</td><td>R3896</td><td>for visible spectral range</td></tr><tr><td>CCD digital camera&amp;nbsp;</td><td>Proscan GmbH, Proscan Special Instruments Ltd. http://www.proscan.de</td><td>HS 101 H</td><td>for visible spectral range</td></tr><tr><td>Control program</td><td>Proscan GmbH, Proscan Special Instruments Ltd. http://www.proscan.de</td><td>PSI line</td><td>for controlling spectral CL measurements with CCD or PMT detectors</td></tr><tr><td>Laptop</td><td>Dell</td><td>Latitude 110L</td><td>hardware for running the control program</td></tr><tr><td>&amp;nbsp;LHe dewar</td><td>cryotherm http://www.cryotherm.de/</td><td>Stratos 100 SL</td><td>container for cryogenic</td></tr><tr><td>LN2 dewar</td><td></td><td></td><td>container for cryogenic</td></tr><tr><td>Protective glasses</td><td>pulsafe</td><td></td><td>protective equipment</td></tr><tr><td>Protective gloves</td><td>tempex</td><td>Protect line&amp;nbsp; Mod. 4081052</td><td>protective equipment</td></tr><tr><td>Heating tape</td><td>Thermocax Isopad GmbH http://www.isopad-solutions.com</td><td>IT-TeMS 6</td><td>to prevent or reduce icing of the flexible hoses during cooling</td></tr><tr><td>Diaphragm pump&amp;nbsp;</td><td>Vacuubrand GmbH &amp;amp; Co KG http://www.vacuubrand.com</td><td>ME4</td><td>to provide the flow rate of the cryogenic</td></tr><tr><td>Vacuum accessoires: flexible hoses, seals, locking rings</td><td></td><td></td><td>connectors for cryogenic CL or EBIC set-up</td></tr><tr><td>Specimen current EBIC amplifier</td><td>KE developments / Deben http://deben.co.uk/</td><td>Type 31</td><td>Measuring the EBIC current</td></tr><tr><td>High vacuum chamber with metal evaporation</td><td>customized</td><td></td><td>formation of Schottky contact for EBIC measurements</td></tr><tr><td>Heating plate</td><td>Retsch GmbH http://www.retsch.de</td><td>SG1</td><td>CL sample preparation</td></tr><tr><td>EBSD detector Nordlys</td><td>HKL</td><td></td><td>no more available; can be replaced by the Oxford EBSD detectors NordlysMax3 or NordlysNano</td></tr><tr><td>EBSD acquisition and evaluation software Channel 5</td><td>HKL</td><td></td><td>no more available; can be replaced by the Oxford EBSD Software AZtecHKL</td></tr><tr><td>ccEBSD program ccEBSD_v1.07.exe</td><td>in house written program</td><td></td><td>for use please contact authors</td></tr><tr><td>EBSD interface with remote control system</td><td>Carl Zeiss AG http://www.zeiss.de/microscopy/&amp;nbsp;</td><td></td><td>necessary for the electron beam control and parameter transfer between EBSD system and SEM&amp;nbsp;&amp;nbsp;</td></tr><tr><td>Vibromet2</td><td>Buehler, http://www.buehler.com/&amp;nbsp;</td><td>671635160</td><td>vibratory polisher</td></tr></tbody></table>

comprehensive characterization of extended defects in semiconductor materials by a scanning electron microscope

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications of semiconductor materials. However, it is still under debate how the defect structure determines the band structure, and therefore, the recombination behavior of electron-hole pairs responsible for the optical and electrical properties of the extended defects. The present paper is a survey of procedures for the spatially resolved investigation of structural and of physical properties of extended defects in semiconductor materials with a scanning electron microscope (SEM). Representative examples are given for crystalline silicon. The luminescence behavior of extended defects can be investigated by cathodoluminescence (CL) measurements. They are particularly valuable because spectrally and spatially resolved information can be obtained simultaneously. For silicon, with an indirect electronic band structure, CL measurements should be carried out at low temperatures down to 5 K due to the low fraction of radiative recombination processes in comparison to non-radiative transitions at room temperature. For the study of the electrical properties of extended defects, the electron beam induced current (EBIC) technique can be applied. The EBIC image reflects the local distribution of defects due to the increased charge-carrier recombination in their vicinity. The procedure for EBIC investigations is described for measurements at room temperature and at low temperatures. Internal strain fields arising from extended defects can be determined quantitatively by cross-correlation electron backscatter diffraction (ccEBSD). This method is challenging because of the necessary preparation of the sample surface and because of the quality of the diffraction patterns which are recorded during the mapping of the sample. The spatial resolution of the three experimental techniques is compared.

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Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope

The optical, electrical, and structural properties of dislocations and of grain boundaries in semiconductor materials can be determined by experiments performed in a scanning electron microscope. Electron microscopy has been used to investigate cathodoluminescence, electron beam induced current, and diffraction of backscattered electrons.

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications ...

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13.6K Views.  Technische Universität Dresden. The optical, electrical, and structural properties of dislocations and of grain boundaries in semiconductor materials can be determined by experiments performed in a scanning electron microscope. Electron microscopy has been used to investigate cathodoluminescence, electron beam induced current, and diffraction of backscattered electrons. 

Video: Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope

Scanning-probe Single-electron Capacitance Spectroscopy

The integration of low-temperature scanning-probe techniques and single-electron capacitance spectroscopy represents a powerful tool to study the electronic quantum structure of small systems - including individual atomic dopants in semiconductors. Here we present a capacitance-based method, known as Subsurface Charge Accumulation (SCA) imaging, which is capable of resolving single-electron charging while achieving sufficient spatial resolution to image individual atomic dopants. The use of a capacitance technique enables observation of subsurface features, such as dopants buried many nanometers beneath the surface of a semiconductor material1,2,3. In principle, this technique can be applied to any system to resolve electron motion below an insulating surface.
As in other electric-field-sensitive scanned-probe techniques4, the lateral spatial resolution of the measurement depends in part on the radius of curvature of the probe tip. Using tips with a small radius of curvature can enable spatial resolution of a few tens of nanometers. This fine spatial resolution allows investigations of small numbers (down to one) of subsurface dopants1,2. The charge resolution depends greatly on the sensitivity of the charge detection circuitry; using high electron mobility transistors (HEMT) in such circuits at cryogenic temperatures enables a sensitivity of approximately 0.01 electrons/Hz&frac12; at 0.3 K 5.

Scanning-probe single-electron capacitance spectroscopy facilitates the study of single-electron motion in localized subsurface regions. A sensitive charge-detection circuit is incorporated into a cryogenic scanning probe microscope to investigate small systems of dopant atoms beneath the surface of semiconductor samples.

The integration of low-temperature scanning-probe techniques and single-electron capacitance spectroscopy represents a powerful tool to study the ...

Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging (ECCI) in a scanning electron microscope (SEM). ECCI allows for imaging of defects and crystallographic features under specific diffraction conditions, similar to that possible via plan-view transmission electron microscopy (PV-TEM). A particular advantage of the ECCI technique is that it requires little to no sample preparation, and indeed can use large area, as-produced samples, making it a considerably higher throughput characterization method than TEM. Similar to TEM, different diffraction conditions can be obtained with ECCI by tilting and rotating the sample in the SEM. This capability enables the selective imaging of specific defects, such as misfit dislocations at the GaP/Si interface, with high contrast levels, which are determined by the standard invisibility criteria. An example application of this technique is described wherein ECCI imaging is used to determine the critical thickness for dislocation nucleation for GaP-on-Si by imaging a range of samples with various GaP epilayer thicknesses. Examples of ECCI micrographs of additional defect types, including threading dislocations and a stacking fault, are provided as demonstration of its broad, TEM-like applicability. Ultimately, the combination of TEM-like capabilities &#8211; high spatial resolution and richness of microstructural data &#8211; with the convenience and speed of SEM, position ECCI as a powerful tool for the rapid characterization of crystalline materials.

The use of electron channeling contrast imaging in a scanning electron microscope to characterize defects in III-V/Si heteroexpitaxial thin films is described. This method yields similar results to plan-view transmission electron microscopy, but in significantly less time due to lack of required sample preparation.

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging ...

In Depth Analyses of LEDs by a Combination of X-ray Computed Tomography (CT) and Light Microscopy (LM) Correlated with Scanning Electron Microscopy (SEM)

In failure analysis, device characterization and reverse engineering of light emitting diodes (LEDs), and similar electronic components of micro-characterization, plays an important role. Commonly, different techniques like X-ray computed tomography (CT), light microscopy (LM) and scanning electron microscopy (SEM) are used separately. Similarly, the results have to be treated for each technique independently. Here a comprehensive study is shown which demonstrates the potentials leveraged by linking CT, LM and SEM. In depth characterization is performed on a white emitting LED, which can be operated throughout all characterization steps. Major advantages are: planned preparation of defined cross sections, correlation of optical properties to structural and compositional information, as well as reliable identification of different functional regions. This results from the breadth of information available from identical regions of interest (ROIs): polarization contrast, bright and dark-field LM images, as well as optical images of the LED cross section in operation. This is supplemented by SEM imaging techniques and micro-analysis using energy dispersive X-ray spectroscopy.

In Depth Analyses of LEDs by a Combination of X-ray Computed Tomography CT and Light Microscopy LM Correlated with Scanning Electron Microscopy SEM

A workflow for comprehensive micro-characterization of active optical devices is outlined. It contains structural as well as functional investigations by means of CT, LM and SEM. The method is demonstrated for a white LED which can be still be operated during characterization.

In failure analysis, device characterization and reverse engineering of light emitting diodes (LEDs), and similar electronic components of ...

Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics

This paper reports an array-designed C84-embedded Si substrate fabricated using a controlled self-assembly method in an ultra-high vacuum chamber. The characteristics of the C84-embedded Si surface, such as atomic resolution topography, local electronic density of states, band gap energy, field emission properties, nanomechanical stiffness, and surface magnetism, were examined using a variety of surface analysis techniques under ultra, high vacuum (UHV) conditions as well as in an atmospheric system. Experimental results demonstrate the high uniformity of the C84-embedded Si surface fabricated using a controlled self-assembly nanotechnology mechanism, represents an important development in the application of field emission display (FED), optoelectronic device fabrication, MEMS cutting tools, and in efforts to find a suitable replacement for carbide semiconductors. Molecular dynamics (MD) method with semi-empirical potential can be used to study the nanoindentation of C84-embedded Si substrate. A detailed description for performing MD simulation is presented here. Details for a comprehensive study on mechanical analysis of MD simulation such as indentation force, Young&#39;s modulus, surface stiffness, atomic stress, and atomic strain are included. The atomic stress and von-Mises strain distributions of the indentation model can be calculated to monitor deformation mechanism with time evaluation in atomistic level.

Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics

This paper reports the nanomaterial fabrication of a fullerene Si substrate inspected and verified by nanomeasurements and molecular dynamic simulation.

This paper reports an array-designed C84-embedded Si substrate fabricated using a controlled self-assembly method in an ultra-high vacuum chamber. The ...

Characterization of Ultra-fine Grained and Nanocrystalline Materials Using Transmission Kikuchi Diffraction

One of the challenges in microstructure analysis nowadays resides in the reliable and accurate characterization of ultra-fine grained (UFG) and nanocrystalline materials. The traditional techniques associated with scanning electron microscopy (SEM), such as electron backscatter diffraction (EBSD), do not possess the required spatial resolution due to the large interaction volume between the electrons from the beam and the atoms of the material. Transmission electron microscopy (TEM) has the required spatial resolution. However, due to a lack of automation in the analysis system, the rate of data acquisition is slow which limits the area of the specimen that can be characterized. This paper presents a new characterization technique, Transmission Kikuchi Diffraction (TKD), which enables the analysis of the microstructure of UFG and nanocrystalline materials using an SEM equipped with a standard EBSD system. The spatial resolution of this technique can reach 2 nm. This technique can be applied to a large range of materials that would be difficult to analyze using traditional EBSD. After presenting the experimental set up and describing the different steps necessary to realize a TKD analysis, examples of its use on metal alloys and minerals are shown to illustrate the resolution of the technique and its flexibility in term of material to be characterized.

This paper provides a detailed method to characterize the microstructure of ultra-fine grained and nanocrystalline materials using a scanning electron microscope equipped with a standard electron backscatter diffraction system. Metal alloys and minerals presenting refined microstructures are analyzed using this technique, showing the diversity of its possible applications.

One of the challenges in microstructure analysis nowadays resides in the reliable and accurate characterization of ultra-fine grained (UFG) and ...

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and forging. Adoption of this technique is proceeding despite disagreement concerning the underlying mechanism responsible for EAD. The experimental procedure described herein enables a more explicit study compared to previous EAD research by removing thermal effects, which are responsible for disagreement in interpreting previous EAD results. Furthermore, as the procedure described here enables EAD observation in situ and in real time in a transmission electron microscope (TEM), it is superior to existing post-mortem methods that observe EAD effects post-test. Test samples consist of a single crystal copper (SCC) foil having a free-standing tensile test section of nanoscale thickness, fabricated using a combination of laser and ion beam milling. The SCC is mounted to an etched silicon base that provides mechanical support and electrical isolation while serving as a heat sink. Using this geometry, even at high current density (~3,500 A/mm2), the test section experiences a negligible temperature increase (&#60;0.02 &#176;C), thus eliminating Joule heating effects. Monitoring material deformation and identifying the corresponding changes to microstructures, e.g. dislocations, are accomplished by acquiring and analyzing a series of TEM images. Our sample preparation and in situ experiment procedures are robust and versatile as they can be readily utilized to test materials with different microstructures, e.g., single and polycrystalline copper.

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Isolating electrical and thermal effects on electrically assisted deformation (EAD) is very difficult using macroscopic samples. Metallic sample micro- and nanostructures together with a custom test procedure have been developed to evaluate the impact of applied current on the formation without joule heating and evolution of dislocations on these samples.

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and ...

All-electronic Nanosecond-resolved Scanning Tunneling Microscopy: Facilitating the Investigation of Single Dopant Charge Dynamics

The miniaturization of semiconductor devices to scales where small numbers of dopants can control device properties requires the development of new techniques capable of characterizing their dynamics. Investigating single dopants requires sub-nanometer spatial resolution, which motivates the use of scanning tunneling microscopy (STM). However, conventional STM is limited to millisecond temporal resolution. Several methods have been developed to overcome this shortcoming, including all-electronic time-resolved STM, which is used in this study to examine dopant dynamics in silicon with nanosecond resolution. The methods presented here are widely accessible and allow for local measurement of a wide variety of dynamics at the atomic scale. A novel time-resolved scanning tunneling spectroscopy technique is presented and used to efficiently search for dynamics.

We demonstrate an all-electronic method to observe nanosecond-resolved charge dynamics of dopant atoms in silicon with a scanning tunneling microscope.

The miniaturization of semiconductor devices to scales where small numbers of dopants can control device properties requires the development of new ...

Quantitative Atomic-Site Analysis of Functional Dopants/Point Defects in Crystalline Materials by Electron-Channeling-Enhanced Microanalysis

A novel elemental and chemical analysis scheme based on electron-channeling phenomena in crystalline materials is introduced, where the incident high-energy electron beam is rocked with the submicrometric pivot point fixed on a specimen. This method enables us to quantitatively derive the site occupancies and site-dependent chemical information of impurities or intentionally doped functional elements in a specimen, using energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy attached to a scanning transmission electron microscope, which is of significant interest to current materials science, particularly related to nanotechnologies. This scheme is applicable to any combination of elements even when the conventional Rietveld analysis by X-ray or neutron diffraction occasionally fails to provide the desired results because of limited sample sizes and close scattering factors of neighboring elements in the periodic table. In this methodological article, we demonstrate the basic experimental procedure and analysis method of the present beam-rocking microanalysis.

We provide a general outline of quantitative microanalysis methods for estimating the site occupancies of impurities and their chemical states by taking advantage of electron-channeling phenomena under incident electron beam-rocking conditions, which reliably extract information from minority species, light elements, oxygen vacancies, and other point/line/planar defects.

A novel elemental and chemical analysis scheme based on electron-channeling phenomena in crystalline materials is introduced, where the incident ...

Chemistry

A Virtual Simulation Experiment of Mechanics: Material Deformation and Failure Based on Scanning Electron Microscopy

This work presents a set of comprehensive virtual experiments to detect material deformation and failure. The most commonly used pieces of equipment in mechanics and material disciplines, such as a metallographic cutting machine and a high-temperature universal creep testing machine, are integrated into a web-based system to provide different experimental services to users in an immersive and interactive learning environment. The protocol in this work is divided into five subsections, namely, the preparation of the materials, molding the specimen, specimen characterization, specimen loading, nanoindenter installation, and SEM in situ experiments, and this protocol aims to provide an opportunity for users regarding the recognition of different equipment and the corresponding operations, as well as the enhancement of laboratory awareness, etc., using a virtual simulation approach. To provide clear guidance for the experiment, the system highlights the equipment/specimen to be used in the next step and marks the pathway that leads to the equipment with a conspicuous arrow. To mimic the hands-on experiment as closely as possible, we designed and developed a three-dimensional laboratory room, equipment, operations, and experimental procedures. Moreover, the virtual system also considers interactive exercises and registration before using chemicals during the experiment. Incorrect operations are also allowed, resulting in a warning message informing the user. The system can provide interactive and visualized experiments to users at different levels.

This work presents a three-dimensional virtual simulation experiment for material deformation and failure that provides visualized experimental processes. Through a set of experiments, users can become familiar with the equipment and learn the operations in an immersive and interactive learning environment.

This work presents a set of comprehensive virtual experiments to detect material deformation and failure. The most commonly used pieces of equipment in ...

Surface Defects in NiTi Files After Single and Multiple Uses in Endodontic Retreatment

Scanning Electron Microscopic Evaluation of Surface Defects of Remover Retreatment File After Single and Multiple Uses

This study aimed to evaluate surface defects of Remover rotary Nickel-Titanium (NiTi) files after single and multiple uses in conventional endodontic retreatment procedures using scanning electron microscopy (SEM). Eighty acrylic blocks, simulating root canals with a 1.5 mm internal diameter, a 5 mm radius of curvature, and a 55&#176; curvature, were utilized. After chemomechanical preparation and obturation, 24 new Remover files (N30, 7%, L23) were randomly assigned to three groups: single use, triple use, and six uses. The files were operated at 600 rpm with a torque of 2.5 Ncm, cleaned, and sterilized after each use.
SEM analysis at magnifications of 100x, 250x, and 500x revealed surface defects, including tip deformation, microcracks, fracture, unwinding, surface pitting, and blade disruption. Deformation was observed in 75% of the files after a single use and in 100% of the files after three and six uses. Microcracks were absent after single use but appeared in 25% and 87.5% of files after three and six uses, respectively, showing a statistically significant increase (p &#60; 0.001). Surface pitting also significantly increased among groups (p = 0.004).
No fractures were observed in any group. The most common defects were tip deformation (91.7%) and surface pitting (70.8%). The findings suggest that repeated use of NiTi files significantly increases surface defects, elevating the risk of fatigue fractures. Thus, the results recommend limiting the reuse of Remover files to a maximum of 3x. Further research is needed to correlate defect types with anatomical factors and to assess file effectiveness in retreatment scenarios.

Here, we present a protocol for evaluating the surface characteristics of endodontic retreatment files after repeated use in retreatment procedures, utilizing scanning electron microscopy to identify and analyze potential surface defects.

This study aimed to evaluate surface defects of Remover rotary Nickel-Titanium (NiTi) files after single and multiple uses in conventional endodontic ...

Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope

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