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Nanoscale subsurface characterization technologies based on the scanning electron microscope platform offer incomparable advantages of nondestructiveness and penetration depths up to the micrometer scale. However, the electron beam can serve not just as a mechanical/electrical excitation source but also as an excellent nanoscale thermal excitation source, which can facilitate the development of nanoscale subsurface imaging methods based on the Seebeck effect in semiconducting materials. In this work, a subsurface nondestructive imaging technology, scanning thermoelectric capacitance microscopy (STeCM), was developed based on the interaction between a non-steady-state electron beam and semiconducting materials, exploiting the Seebeck effect. In STeCM, a square wave-modulated hot electron beam with huge kinetic energy excites a "thermal wave" in the subsurface local region of the semiconducting sample. The heated local region, acting as a thermoelectric capacitor, undergoes cyclic charging and discharging, leading to the generation of periodic current due to non-equilibrium carrier migration. The second-order harmonic component of this current is demodulated to visualize embedded local thermal/thermoelectric inhomogeneities. Amazingly, for STeCM sample, only a smooth or polished surface is required, eliminating the need for any microfabrication, which will effectively decrease the configuration difficulty in the experiment. STeCM offers an alternative subsurface nondestructive imaging technology for more efficient, simple, and robust characterization. [ABSTRACT FROM AUTHOR]

Pulsed electron beams from a photocathode using an InGaN semiconductor have brought selectively scanning technology to scanning electron microscopes, where the electron beam irradiation intensity and area can be arbitrarily selected within the field of view in SEM images. The p-type InGaN semiconductor crystals grown in the metalorganic chemical vapor deposition equipment were used as the photocathode material for the electron beam source after the surface was activated to a negative electron affinity state in the electron gun under ultrahigh vacuum. The InGaN semiconductor photocathode produced a pulsed electron beam with a rise and fall time of 3 ns, consistent with the time structure of the irradiated pulsed laser used for the optical excitation of electrons. The InGaN photocathode-based electron gun achieved a total beam operation time of 1300 h at 15 μA beam current with a downtime rate of 4% and a current stability of 0.033% after 23 cycles of surface activation and continuous beam operation. The InGaN photocathode-based electron gun has been installed in the conventional scanning electron microscope by replacing the original field emission gun. SEM imaging was performed by selective electron beaming, in which the scanning signal of the SEM system was synchronized with the laser for photocathode excitation to irradiate arbitrary regions in the SEM image at arbitrary intensity. The accuracy of the selection of regions in the SEM image by the selective electron beam was pixel by pixel at the TV scan speed (80 ns/pix, 25 frame/s) of the SEM. [ABSTRACT FROM AUTHOR]

Electron beam induced current (EBIC) measurements provide a powerful tool for characterizing semiconductor based materials and devices. By measuring the current generated by the electron beam of a scanning electron microscope (SEM), EBIC allows us to extract the minority carrier diffusion length (L) and the surface recombination velocity to diffusivity ratio (S/D) of a material. When combined with information on minority carrier lifetime (τ), for instance from time-resolved photoluminescence measurements, the minority carrier mobility of the material can be extracted. However, the EBIC technique relies heavily on the accurate modeling of the carrier generation and collection process. Traditionally, this was achieved using a combination of empirical analytical expressions (and later Monte Carlo simulations) for carrier generation and analytical diffusion/ recombination expressions for carrier collection. This approach introduces significant uncertainties into the extracted material parameters. Here, we present a numerical approach to EBIC modeling which improves the spatial resolution of our model, while also retaining information regarding the relative EBIC signal as a function of incident beam energies and currents. We apply this technique to investigate the temperature dependent minority carrier mobility of InAs/InAsSb and InGaAs/ InAsSb strained layer superlattice infrared detectors and compare our results to the values obtained using external quantum efficiency measurements of the same samples. Our approach not only allows for an improvement in the uncertainty of the extracted material parameters, but also offers insight into the material and device behavior as a function of nonequilibrium carrier concentration. The technique presented here offers potentially improved characterization of not only infrared detectors, but a range of semiconductor-based devices. [ABSTRACT FROM AUTHOR]

The fraction R of charges undergoing discharge during the time separating two electron pulses is derived from the induced current method developed in a scanning electron microscope. Irradiation is performed via a 10 keV defocused electron beam and low current density. The evolution of R with temperature (in the range 300-663 K) obeys to an Arrhenius type relation. Activation energies connected with the processes involved are deduced. In sapphire, no discernible discharge is observed due to the dominance of deep traps. In silver doped sapphire, R increases sharply from 10% to 70% as the temperature rises from 360 to 420 K, with a corresponding activation energy of 0.51 eV. In contrast, in polycrystalline alumina processed by solid state sintering (grain diameters of 1.7, 2.7, and 4.5 μm) the degree of discharge increases continuously with temperature and grain size. The enhancement with grain size indicates that the sintering conditions influence strongly the efficiency of a gettering effect. The activation energy below 573 K is about 0.12 eV independently of grain size. Above 573 K, a second activation energy of 0.26 eV appears for the smallest grain size sample. The results suggest that discharge may stem from a density of trapping states, associated to grain boundaries in sintered samples, rather than from a single trapping level linked to the doping element as Ag in sapphire. [ABSTRACT FROM AUTHOR]

The aligned CdS nanorods are obtained by dispersing CdS in the conducting polyaniline matrix. The rods are about 50 nm in diameter and 400 nm in length. The significant changes of electronic absorption spectra of CdS nanorods and conducting polyaniline indicate the strong interaction between them. CdS—Polyaniline nanocomposites exhibit a three-dimensional Mott’s hopping process in the electrical conduction. Temperature variation of frequency dependent conductivity implies the correlated barrier hopping. The barrier height increases with the content of CdS. [ABSTRACT FROM AUTHOR]

We investigated the thermal stability of a N-incorporated amorphous Hf silicate film in terms of Hf diffusion in the film using high-angle annular-dark-field scanning transmission electron microscopy. We first examined HfxSi1-xO2 (x=0.5,1.0) films with and without N incorporation. Our analysis showed that N incorporation (15 at. % of N) into the Hf0.5Si0.5O2 film significantly suppressed chemical component separation during annealing at 1000 °C. In contrast, clear separation of Hf-rich and Hf-poor (SiO2-rich) regions occurred in the Hf0.5Si0.5O2 film without N incorporation. In addition, HfO2 crystalline particle formation was observed in the HfO2 films with and without N incorporation (25 at. % of N). These results strongly suggest that Si–N bonding in the N-incorporated Hf0.5Si0.5O2 film, rather than Hf–N chemical bonding, is the main cause of the suppression of the chemical component separation and HfO2 crystallization. Second, we examined Hf diffusion in a SiO2 film with and without N incorporation and found that the N incorporation significantly reduced the Hf diffusion. We therefore infer that the suppression of the chemical component separation in the N-incorporated Hf silicate film can be explained in terms of the suppression of Hf diffusion by the Si–O, N network in the N-incorporated Hf silicate film. [ABSTRACT FROM AUTHOR]

The time evolution of gallium nitride quantum dots luminescence has been recorded in situ in a scanning electron microscope. Electrons of 10 keV were injected in a stationary spot in a scanning electron microscope during 30 min. Two different regimes were evidenced depending on the beam current density. At low density, the cathodoluminescence (CL) intensity decreased rapidly and a dark spot appeared. At high beam density, the CL intensity decrease was slower, and a dark ring centered on the beam injection location was formed. All the results are coherently interpreted by an enhanced diffusion of nonradiative defects promoted by nonradiative recombinations. [ABSTRACT FROM AUTHOR]

Porous silicon carbide fabricated from p-type 4H and 6H SiC wafers by electrochemical etching in hydrofluoric electrolyte is studied. An investigation of the dependence on wafer polarity reveals that pore formation is favored on the C face while complete dissolution occurs on the Si face. When the etching is done on the C face, the pore wall thickness decreases with increasing current density. The morphology of the front surface of the sample depends on the prior treatment of the workpiece surface. The porosity is estimated based on the analysis of scanning electron microscope images, charge-transfer calculations, and gravimetric analysis. [ABSTRACT FROM AUTHOR]

Cathodoluminescence (CL) in the scanning electron microscope (SEM) has been used to investigate the luminescence mechanisms in tin oxide. Sintered material prepared from high purity powder has been found to show a strong dependence of the CL emission on the thermal treatments applied during sample preparation. SEM images show the presence of nano and microcrystalline grains. The correlation of the grain size and morphology with the optical emission is analyzed by CL microscopy and spectroscopy. The main emission bands appear centered at about 2.58, 2.25, and 1.94 eV depending on the sintering treatment. CL images reveal that the 2.25 and the 2.58 eV bands are associated at specific crystal faces. The evolution of the luminescence bands with mechanical milling shows a complex evolution of the 1.94 and 2.58 eV emissions which is explained by formation and recovery of defects during milling. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Two-dimensional dopant mapping using secondary electrons in a scanning electron microscope (SEM) is a useful and rapid technique for studying dopant distributions with high spatial resolution in semiconductor materials and devices. However, the technique has a major drawback: although p-n junctions and differently doped p-type regions can be imaged, the contrast from differently doped n-type regions is extremely low, hence, such regions cannot normally be detected. We demonstrate that energy filtering of the secondary electrons substantially enhances the contrast of differently doped n-type regions, so that they are easily differentiated and mapped. This is because the contrast is based on the shift of energy spectra from n and p regions rather than secondary electron yield differences that lead to the conventional dopant contrast. We have used a standard commercially available Schottky field emission gun SEM for our work. Energy-filtered secondary electron imaging in a SEM therefore provides a rapid technique for the imaging and mapping of both p-type and n-type dopants. Our initial results indicate that a spatial resolution of <6 nm can be expected for favorable specimens. [ABSTRACT FROM AUTHOR]

Presents a study which analyzed transient cathodoluminescence of semiconductors in a scanning electron microscope. Method of the study; Results and discussion; Conclusion.

Deals with a study which measured the electron densities in CH[sub4]/H[sub2]/Ar and CCl[sub2]F[sub2]/O[sub2] electron cyclotron resonance discharges of semiconductors. Experimentation details; Assessment on surface morphologies through scanning electron microscopy; Functions of microwave power.

Electron channeling contrast imaging (ECCI) is emerging as a technique for rapid and highresolution characterization of individual crystalline defects in a scanning electron microscope. However, the application of ECCI to semiconductor materials has been limited to bare samples in plan-view geometry. In this paper, two modalities of this technique are demonstrated with relevance to semiconductor manufacturing and failure analysis: (1) The use of ECCI to reveal misfit dislocation defects along a cleaved cross-section of a SiGe compositionally graded buffer grown on Si and (2) plan-view imaging of misfit dislocations in metamorphic SiGe/Si layers covered by amorphous oxide layers, where the partial loss of contrast due to the oxide layers is quantified and the effect of the beam accelerating voltage is studied. These results demonstrate the power of ECCI in inspecting crystallographic defects non-destructively over large areas, which is highly desirable for substrate quality control in manufacturing of products based on crystalline materials. [ABSTRACT FROM AUTHOR]

Electric field induced mechanical resonances of In2O3 microrods are studied by in-situ measurements in the chamber of a scanning electron microscope. Young's moduli of rods with different cross-sectional shapes are calculated from the resonance frequency, and a range of values between 131 and 152GPa are obtained. A quality factor of 1180-3780 is measured from the amplitude-frequency curves, revealing the suitability of In2O3 microrods as micromechanical resonators. The Young's modulus, E, of one of the rods is also measured from the elastic response in the force-displacement curve recorded in an atomic force microscope. E values obtained by in-situ scanning electron microscopy and by atomic force microscopy are found to differ in about 8%. The results provide data on Young's modulus of In2O3 and confirm the suitability of in-situ scanning electron microscopy mechanical resonance measurements to investigate the elastic behavior of semiconductor microrods. [ABSTRACT FROM AUTHOR]

With assistance from a nano-manipulator system inside a scanning electron microscope chamber, mechanical and electrical properties of ZnO nanorings were investigated. The change of a fractured nanoring to nearly straight nanobelts was strong evidence to support the previously proposed electrostatic-force-induced self-coiling model, and our computational simulation results indicated the fracture force was 25-30 μN. The contact between a tungsten tip of the manipulator and a ZnO nanoring was confirmed as the Schottky type; therefore, the change of I-V curves of the nanoring under compression was attributed to the Schottky barrier height changes. [ABSTRACT FROM AUTHOR]

Further scaling of semiconductor devices is limited by the increasing number of defects in contact- or via-holes that occur as the aspect ratio increases. Inspection of the bottom of a via-hole, to check for complete clearance, becomes problematical for aspect ratios greater than about 5. Such an inspection is extremely important to circuit yield, as any residue in the hole will result in device failure. At present, holes are inspected from the top using conventional scanning electron microscope imaging, but this method is ineffective for hole diameters <100 nm. Smaller holes need to be observed by this method in cross section to ensure clearance; a method that is not suitable for manufacturing. To resolve the problem, the authors propose a novel method of inspecting small contact/via-holes using a low voltage microcolumn, where the image formed by the specimen current is very sensitive to the presence of residues in the hole. Simply when the beam is place over the hole, the presence of a residual thin film at the bottom of the hole can be reliably detected simply by measuring the sample current due to a stationary electron probe. This inspection method is been demonstrated with a patterned SiO2 layer on a Si substrate. Preliminary results for currents measured from this sample show that the Si substrate and the SiO2 residual layer are clearly distinguished. The inspection method and test results for a submicrometer pattern will be discussed in detail. [ABSTRACT FROM AUTHOR]

Accurate measurement of linewidth is a critical problem in sub-100 nm semiconductor manufacturing, where required accuracy is below 1 nm. Critical dimension scanning electron microscopes (CD-SEMs) are usually used for such measurements. A cross correlation of CD-SEMs, while demonstrating a good relative trend, is often subjected to a significant absolute linewidth error. There is no proven algorithm for absolute edge detection in CD-SEMs. In this article, the authors demonstrate that edge detection depends greatly on parameters of SEM settings, such as beam diameter, and pattern properties, such as the wall angle of a pattern. When both the signal and pattern are known, an offset for a specific SEM algorithm can be found. An algorithm for automatic edge detection in CD-SEMs can be tuned for beam parameters and the type of pattern. A SEM signal was simulated using the advanced Monte Carlo software CHARIOT. Input data for the modeling were three dimensional microstructures and e-beam parameters. A known pattern was then compared to a simulated signal. Such a comparison allowed to define the edge position and calibrate a SEM so that any system- and pattern-dependent errors could be removed. [ABSTRACT FROM AUTHOR]

An analysis is given of a symmetric secondary electron extraction system suitable for use in a newly proposed immersion lens. The detailed behavior of secondary electrons in the combined electrostatic and magnetic field is presented. Numerical results show that this extraction system imposes very small effects on the primary electrons yet retains a high collection efficiency on secondary electrons, so that the advantages of the low aberration immersion lens can be fully utilized. [ABSTRACT FROM AUTHOR]

CuI is used to control the molecular orientation of copper phthalocyanine (CuPc) and modify the anodes in organic solar cells based on CuPc/C60. By introducing a CuI buffer between indium tin oxide and CuPc, the power conversion efficiency is significantly enhanced by a factor of ∼70%. Because of the strong interactions between the CuI and CuPc, the stacking orientation of CuPc molecules is changed, resulting in a ∼65% increase in absorption coefficient, a larger carrier mobility and a smoother film surface. The anode work function is raised by the formation of a dipole layer. [ABSTRACT FROM AUTHOR]

We investigated the stability of ZnO nanowires in a metal-semiconductor-metal structure by applying a longitudinal electric field inside a scanning electron microscope equipped with manipulators. The electrical transport was well simulated by the thermionic-field-emission model and the failure of single crystalline ZnO nanowires was directly observed when the applied electric field reached the break point, an electric field intensity of ∼106 V/m. The recrystallization of ZnO nanowires from single crystalline to polycrystalline pearl-like structure in the failure process was also investigated. Experimental results indicated that the failure is attributed to a joint effect of high electric field and Joule heating. [ABSTRACT FROM AUTHOR]

An electron beam (EB) lithography technique to form patterns directly on a semiconductor crystal surface, without using a resist or an oxide film, combined with molecular beam epitaxy (MBE) growth is described for potential applications to site definition of quantum dots. Periodically arranged submicrometer protrusions on a GaAs wafer surface were observed by EB irradiation from a scanning electron microscope with moderately high vacuum. This protrusion has a caldera shape with a concave on the top. On the other hand, when the GaAs was irradiated with an EB, although not well focused, from reflection high energy electron diffraction gun in an ultrahigh vacuum annealing chamber of MBE, a pit with concave shape was obtained. Clear photoluminescence emission was observed from an InAs ultrathin layer overgrown on the pit area. [ABSTRACT FROM AUTHOR]

Direct measurements on electrical characteristics have been carried out in situ inside a scanning electron microscope using a multiple nanoprobe system on individual SnO2 capped ZnO nanowires (NWs) within a NW film on a Zn substrate. It is shown that while good Ohmic contacts can be made at Zn–ZnO NW and ZnO NW–SnO2 cap (when heavily doped with Zn) junctions, the overall I-V characteristics of the Zn–ZnO–SnO2 junction system differ significantly among different NWs, suggesting doping inhomogeneity in the NW film. [ABSTRACT FROM AUTHOR]

Direct imaging of atomic step morphologies and individual threading dislocations in on-axis epitaxial 4H-SiC surfaces is presented. Topographically sensitive electron images of the crystalline surfaces were obtained through forescattered electron detection inside a conventional scanning electron microscope. This technique, termed electron channeling contrast imaging (ECCI), has been utilized to reveal the configuration of highly stepped, homoepitaxial 4H-SiC films grown on 4H-SiC mesa structures. Individual threading dislocations have been consistently imaged at the core of spiral atomic step morphologies located on the 4H-SiC surfaces. The ability of ECCI to image atomic steps was verified by atomic force microscopy. [ABSTRACT FROM AUTHOR]

The unidirectional coupling of a microcavity mode to a ridge waveguide in a slab photonic crystal structure was investigated for the first time. Experimental observation of the coupling efficiency for the signal coupled out of the structure is in good agreement with the result of three-dimensional finite-difference time-domain simulations. The coupling efficiency of the cavity mode to the output channel is ∼60%. [ABSTRACT FROM AUTHOR]

Utilizing a high quality factor (Q∼1.5×106) optical microresonator to provide sensitivity down to a fractional surface optical loss of αs′∼10-7, we show that the optical loss within Si microphotonic components can be dramatically altered by Si surface preparation, with αs′∼1×10-5 measured for chemical oxide surfaces as compared to αs′≤=1×10-6 for hydrogen-terminated Si surfaces. These results indicate that the optical properties of Si surfaces can be significantly and reversibly altered by standard microelectronic treatments, and that stable, high optical quality surface passivation layers will be critical in future Si micro- and nanophotonic systems [ABSTRACT FROM AUTHOR]

We prepared W–Ga–C composite contacts on W–Ga–C composite nanowires by focused-ion-beam-induced chemical vapor deposition using a dual-beam scanning electron microscope/focused-ion-beam system. The current-voltage (I-V) characteristics of wires were found to change from nonlinear to linear with increasing wire thickness. For wires with small dimensions, which result in strong nonlinear I-V behavior at room temperature, pairs of contacts were fabricated along the wire under different ion energies and scanning modes. Nonlinear and asymmetric rectifying I-V characteristics were observed. The results suggest that nanoscaled W–Ga–C nanowires may behave similarly to semiconductors and that the contact characteristics may be modified using different deposition conditions. Furthermore, ohmiclike junctions could be formed through the use of specific deposition conditions for the contact pads and nanowires. [ABSTRACT FROM AUTHOR]

In this letter, the contrast reversal effect in scanning-capacitance-microscopy (SCM) dopant concentration extraction is investigated both theoretically and experimentally. The shift of the turning point in the nonmonotonic response of peak dC/dV signal versus dopant concentration to higher dopant concentrations is explained by the difference of the capture/emission time constant of the interface states and the series resistance of the semiconductor sample. This is verified by comparing the experimental SCM measurements with the simulated peak dC/dV profile on a p-type multiple dopant step sample. The contrast reversal effect, which affects the accuracy of dopant concentration extraction using the SCM peak dC/dV signal, can be minimized by using an overlying oxide with good interfacial quality and a semiconductor sample of low series resistance. [ABSTRACT FROM AUTHOR]

The aberration-corrected scanning transmission electron microscope allows probes to be formed with less than 1-Å diameter, providing sufficient sensitivity to observe individual Hf atoms within the SiO2 passivating layer of a HfO2/SiO2/Si alternative gate dielectric stack. Furthermore, the depth resolution is sufficient to localize the atom positions to half-nanometer precision in the third dimension. From a through-focal series of images, we demonstrate a three-dimensional reconstruction of the Hf atom sites, representing a three-dimensional map of potential breakdown sites within the gate dielectric. [ABSTRACT FROM AUTHOR]

The most common fabrication processes of nanoelectromechanical structures usually start with a silicon-on-insulator chip and incorporate several lithography and etch steps. The wet etch step, which involves hydrofluoric acid, is generally the most critical of these processing steps. In this letter, we present an enhancement of the wet etch step which relies on electron-beam deposition. The technique of electron-beam deposition utilizes a protective carbon layer which is applied by a scanning electron microscope. It allows us to resolve typical problems associated with the wet etch step and drastically increases the yield. [ABSTRACT FROM AUTHOR]

Semiconductor dopant profiling using secondary electron imaging in a scanning electron microscope has been developed in recent years. In this letter, we show that the mechanism behind it also allows mapping of the electric potential of undoped regions. By using an unbiased GaAs/AlGaAs heterostructure, this letter demonstrates the direct observation of the electrostatic potential variation inside a 90-nm-wide undoped GaAs channel surrounded by ionized dopants. The secondary electron emission intensities are compared with two-dimensional numerical solutions of the electric potential. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A novel diagnostic technique utilizing secondary-electron energy analysis in a scanning electron microscope to image modulated photovoltages in semiconductor samples is reported. Contacts to the sample are not required, allowing nondestructive inspection of partially processed devices and isolated regions. Photovoltage decay following pulsed illumination, indicative of material and junction quality, can be observed. Applications to silicon on sapphire, InP, and GaAs devices are described. [ABSTRACT FROM AUTHOR]

Scanning hot electron microscopy (SHEM) has been proposed as an experimental technique which allows for detection of hot electrons emitted from a subsurface semiconductor structure, thus making it possible to obtain the spatial distribution of hot electrons in a device. Here we present the experimental evidence of SHEM operation. Hot electrons with energies of 3 eV are injected by means of a Si/CaF2/Au heterostructure and subsequently detected at the tip of a scanning tunneling microscope in the SHEM configuration. The measured hot electron current was approximately 4 pA for a tunnel current of 5 nA. These results, although still of a preliminary nature, show the potential of SHEM as a technique suitable for the visualization of electron wave effects in semiconductor structures. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a contrast mechanism in ion beam induced charge (IBIC) imaging in semiconductors. Increase in charge collection signals; Function of electron beam on electron beam induced current imaging in a scanning electron microscope; Display of the IBIC image of the collector-substrate junction.