Scanning Capacitance Microscopy Images Research Articles

Characterization of the parasitic masking layer formed during GaN SA-MOVPE using PECVD SiO2 masks

X-ray photoelectron spectroscopy (XPS) was used to study the surface composition of the parasitic masking layer formed during selective area metalorganic vapor phase epitaxy (MOVPE) of gallium nitride (GaN) using silicon dioxide (SiO2) masks deposited by plasma enhanced chemical vapor deposition (PECVD). It was shown that non-stoichiometric silicon oxynitride layer (SiOxNy) is responsible for the inhibition of GaN nucleation in the vicinity of the SiO2 mask. Atomic force microscopy (AFM) was applied to examine the surface topography, whereas scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) techniques were used for the purpose of electrical characterization of the parasitic masking layer. The overgrowth of GaN islands through the discontinuities in the SiOxNy film was shown. The SCM imaging showed the presence of a positive electric charge in the parasitic masking layer, indicating the accumulation of defects in the silicon oxynitride film.

Phosphorus deactivation by hydrogen on hot carrier stressed high-voltage N-channel field effect transistor CMOS device demonstrated by scanning capacitance microscopy imaging

Junction profiles of hot electron stressed high-voltage N-channel field effect transistor (NFET) devices were measured by scanning capacitance microscopy. Deactivation of phosphorous was observed on the drain side. To directly establish a link between phosphorus deactivation and hydrogen, junction profiles were measured on an unstressed NFET (N-type metal-oxide-semiconductor) device with and without H2 plasma treatment and with subsequent 400 °C annealing in helium. Phosphorus deactivation was observed in the device after H2 plasma treatment, while subsequent 400 °C annealing led to dissociation of the P–H (or H–Si–P) bond and recovery of the device junctions.

Demonstration of GaAsSb/InAs nanowire backward diodes grown using position-controlled vapor–liquid–solid method

p-GaAsSb/n-InAs type-II nanowire (NW) diodes were fabricated using the position-controlled vapor–liquid–solid growth method. InAs and GaAsSb NW segments were grown vertically on GaAs(111)B substrates with the assistance of Au catalysts. Transmission electron microscopy-energy-dispersive X-ray spectroscopy analysis revealed that the GaAsSb segments have an Sb content of 40%, which is sufficient to form a tunnel heterostructure. Scanning capacitance microscope images clearly indicated the formation of a p–n junction in the NWs. Backward diode characteristics, that is, current flow toward negative bias originating from a tunnel current and current suppression toward positive bias by a heterobarrier, were demonstrated.

Electrical current at micro-/macro-scale of undoped and nitrogen-doped MWPECVD diamond films

Chemical, structural, morphological and micro-/macro-electrical properties of undoped and nitrogen-(N-)doped diamond films are determined by X-ray photoelectron spectroscopy, Raman and photoluminescence spectroscopies, field emission scanning electron microscopy, atomic force microscopy, scanning capacitance microscopy (SCM) and two points technique for I–V characteristics, respectively. The characterization results are very useful to examine and understand the relationship among these properties.The effect of the nitrogen incorporation in diamond films is investigated through the evolution of the chemical, structural, morphological and topographical features and of the electrical behavior. The distribution of the electrical current is first assessed at millimeter scale on the surface of diamond films and then at micrometer scale on small regions in order to establish the sites where the carriers preferentially move. Specifically, the SCM images indicate a non-uniform distribution of carriers on the morphological structures mainly located along the grain boundaries.A good agreement is found by comparing the electrical currents at the micro- and macro-scale. This work aims to highlight phenomena such as photo- and thermionic emission from N-doped diamond useful for microelectronic engineering.

Unexpected surface implanted layer in static random access memory devices observed by microwave impedance microscope

Real-space mapping of doping concentration in semiconductor devices is of great importance for the microelectronics industry. In this work, a scanning microwave impedance microscope (MIM) is employed to resolve the local conductivity distribution of a static random access memory sample. The MIM electronics can also be adjusted to the scanning capacitance microscopy (SCM) mode, allowing both measurements on the same region. Interestingly, while the conventional SCM images match the nominal device structure, the MIM results display certain unexpected features, which originate from a thin layer of the dopant ions penetrating through the protective layers during the heavy implantation steps.

Contrast distortion induced by modulation voltage in scanning capacitance microscopy

With a dark-mode scanning capacitance microscopy (SCM), we directly observed the influence of SCM modulation voltage (MV) on image contrasts. For electrical junctions, an extensive modulated area induced by MV may lead to noticeable changes in the SCM signal phase and intensity, resulting in a narrowed junction image and a broadened carrier concentration profile. This contrast distortion in SCM images may occur even if the peak-to-peak MV is down to 0.3 V. In addition, MV may shift the measured electrical junction depth. The balance of SCM signals components explain these MV-induced contrast distortions.

Capacitive Imaging of Graphene Flakes on SiO2 Substrate

We used scanning capacitance microscopy (SCM) for the local electrical imaging of graphene flakes on a SiO2 substrate. As a result of analyzing the dependence of the SCM measurements on the area of thin graphite nanoislands together with the observed difference in contrast of SCM images related to the graphene layer's thickness, we have concluded that the SCM measurements can selectively image high-conductivity few-layer graphene (FLG) flakes on an insulating substrate without having to fabricate external electrical contacts on the graphene. Our technique is a simple way to explore the conductive properties of low-dimensional systems on an insulating substrate with nanoscale resolution.

The grain boundary related p-type conductivity in ZnO films prepared by ultrasonic spray pyrolysis

Intrinsic p-type ZnO thin film was fabricated on sapphire substrate by ultrasonic spray pyrolysis, the p-type ZnO film is achieved using O2 as the carrier gas, with a resistivity of 2.18 Ω cm−1, a carrier concentration of 1.10×1016 cm−3, and a high Hall mobility of 261 cm2/V s. The scanning capacitance microscopy images and annealing the p-type ZnO indicate that the absorbed oxygen in the grain boundary (GB) aroused the p-type conductivity, and the high Hall mobility of the p-type ZnO film own to the quasi-two-dimensional hole gas, which was induced by the negatively charged interface states in the GBs.

Local mapping of interface traps in HfSiO/Si structure by scanning capacitance microscopy using dV/dC signal

Scanning capacitance microscopy (SCM) using a dV/dC signal has been proposed for local mapping of interface traps in an insulator/semiconductor structure. In conventional SCM measurements using a dC/dV signal, it is difficult to accurately analyze the spatial distribution of interface traps from the obtained SCM images because the dC/dV signal is inversely proportional to the interface trap density. In the proposed technique, however, the spatial distribution of the interface traps can be characterized using the dV/dC signal, which is directly proportional to the interface trap density. The effectiveness of the proposed technique has been demonstrated by characterizing the spatial distributions of the interface traps in HfSiO/Si structures before and after H2 annealing. The dV/dC images obtained reveal that the spatial variation in the interface trap density is reduced by H2 annealing. Consequently, SCM measurements using a dV/dC signal have been verified to effectively characterize the spatial distribution of interface traps.

Localized Charging Properties of Si Nanocrystals Embedded in a SiO2 Layer by Scanning Capacitance Microscopy

In this work, we characterized charging properties of silicon nanocrystals (NCs) using scanning capacitance microscopy (SCM). The size of the NCs produced by pyrolysis method is in the range of 10–50 nm with a density of around 1011/cm2. Using a conducting tip, a charge was injected directly into the NCs, and the charging characteristics of a NC were analyzed through the dC/dV–V curve shift and SCM images. Bias voltage stress to a NC cause the variation of capacitance due to the electron charging, which is reflected in SCM images. By measuring consecutive dC/dV–V curve shift after NC charging, we also analyzed retention characteristics of a NC. In temperature dependence experiment, NC reveals the characteristics of good chargeability at high temperature. Capacitance spectroscopy and related SCM images show that SCM can be an adequate tool for more detailed analysis of the charging and discharging effects of each NC.

Doping characterization of InAs∕GaAs quantum dot heterostructure by cross-sectional scanning capacitance microscopy

In order to better understand dopant incorporation in quantum dot infrared photodetectors, the application of cross-sectional scanning capacitance microscopy (SCM) has been used to investigate carrier occupation/distribution in a multilayer InAs∕GaAs quantum dot (QD) heterostructure for different doping techniques. The doping schemes in the QD structure include direct doping (in InAs QD layers) and remote doping (in GaAs barrier layers), each with different doping concentrations. The SCM image suggests that large band bending occurs due to highly doped, remote-doping layers, thereby causing electron redistribution in direct-doping layers. The experimental result is supported by a band structure calculation using the Schrödinger–Poisson method by NEXTNANO3.

Probing Carrier Depletions on Grain Boundaries in Polycrystalline Si Thin Films by Scanning Capacitance Microscopy

ABSTRACTGrain boundaries (GBs) in polycrystalline Si thin-film solar cells are believed to limit the photovoltaic efficiencies. In this paper, we report on a nanometer-resolution measurement of the carrier depletion at the GBs, using scanning capacitance microscopy (SCM). The SCM images exhibit the following features: (1) Carrier concentrations are lower at locations around the GBs than on center regions of the grains; (2) The depletion width at the GBs varies considerably, between 0 and 100 nm, depending on individual GBs; (3) Intra-grain carrier depletion was also observed at point and line defects; and (4) The faceted features that were observed on the topography of the as-grown film surface appeared on the SCM images even after the film surface was polished flat. The direct measurement of the carrier depletion on the GBs demonstrates that the GBs in Si thin films indeed create charged gap states. The nonuniformity of the carrier depletions suggests that the gap states depend on specific GB structures, which should relate directly to the grain orientations and grain facets adjacent to the GB. The depletion around the intragrain defects indicates that the defects are charged and can be recombination centers, and thus, harmful to device performance. This paper reports the first step of our studies toward understanding the relationships between the electronic and structural properties on specific GBs.

Characterization of Al-doped ZnTe layer using scanning capacitance microscopy and Kelvin probe force microscopy

Al-doped ZnTe layer in ZnTe LED fabricated by Al thermal diffusion has been characterized using cross-sectional scanning capacitance microscopy (SCM) and Kelvin probe force microscopy (KFM), and the results were verified by comparing with the result of the electron beam induced current (EBIC) measurements. Both SCM and KFM images showed contrast changes between Al diffusion layer and p-type substrate, indicating the conductivity type conversion in ZnTe. The distance from the surface of ZnTe to the contrast change position was around 1.8 μm, in consistent with the result of EBIC measurement. The surface potential of the Al diffusion layer was found to be almost constant, implying that the diffusion layer is relatively homogenous in depth direction. Thus, SCM and KFM are capable of providing the electrical information on ZnTe LED.

Scanning capacitance microscopy and the role of localized charges in dielectric films: Infering or challenging?

Scanning capacitance microscopy (SCM) is considered a suitable technique to examine dopant profiles and to provide images of the charge carrier distribution in real device structures. A drawback of the application is the sensitivity of the method to different kinds of charges in the surface passivation layer. For a systematic study silicon structures with stripe patterns of different doping concentrations, covered either by a native oxide or by a thermally grown silicondioxide layer, were examined. The dependence of the d C/d V characteristic on the sweep rate of the tip bias and on the bias sweep direction was analyzed. Local charge trapping in the passivation layer was estimated from shifts of the peak position of the d C/d V versus V curves. It is demonstrated as to how features related to the charge trapping in the passivation layer and induced by a certain dc bias at the tip superimpose the dopant related features in the SCM image.

Charge storage in silicon-implanted silicondioxide layers examined by scanning probe microscopy

Ion beam synthesis is a promising technique to generate embedded nanoclusters in thin insulating layers for prospective memory devices. At present the electronic structure of clusters in oxide layers and the respective charge storage mechanism are not well understood. Moreover, it is still unclear, whether cluster-related or damage-related states in the silica network are predominant. Here, we report on the charge trapping in silicon implanted SiO 2 layers using scanning capacitance microscopy and scanning force microscopy. Silicondioxide layers on (100) oriented silicon with a thickness of 25 nm were silicon implanted with different doses and subsequently annealed at high temperatures (1050 °C/1150 °C). Charge injection into the insulating layer was accomplished by applying a bias between the conductive probing tip and the substrate. Local as well as scanning injection in quadratic areas was performed in the contact mode. Scanning capacitance microscopy images taken at different times after injection show the charge patterns and their retention characteristics. For a quantitative estimate of the trapped oxide charge densities the peak shifts of the local d C / d V curves were evaluated. The strongest trapping effect was found for heavily silicon-implanted (2 × 10 16 cm - 2 ) SiO 2 on p-substrate. Complementary information about local charge trapping was obtained from scanning force microscopy images. Sequences of voltages with different polarity were used to study the trapping/ detrapping kinetics and allowed a comparison of the degradation and the programmability of the different oxide layers.

Study of two-dimensional B doping profile in Si fin field-effect transistor structures by high angle annular dark field in scanning transmission electron microscopy mode

High angle annular dark field in scanning transmission electron microscopy mode is used to characterize the two-dimensional B dopant profile of Si fin field-effect transistor nanostructures. We attribute the enhanced intensity in the images to the strain fields produced by the substitutional B atoms in the Si lattice. Two different doping cases were studied, with an increment in the ion dose level. The observed doping profiles were compared with scanning capacitance microscopy images and with computer simulations of the same structures. All results show excellent qualitative agreement. High resolution transmission electron microscopy, electron energy-loss spectroscopy, and energy-dispersive spectroscopy analyses were also performed on these samples and were instrumental in identifying Cu nanoparticle contamination in the prepared transmission electron microscopy samples.

Electrical Properties of a Silicon Nanocrystal Embedded in a Thin Oxide Layer

Electrostatic force microscopy (EFM) and scanning capacitance microscopy (SCM) were used to probe electrically silicon nanocrystals (NCs) deposited on an insulating layer. NC samples were produced by aerosol techniques followed by a sharpening oxidation. The size of the NCs is in the range of 10–50 nm with a density of around 1011/cm2. Using a conducting tip, a charge was injected directly into the NCs, and the bias-dependent images resulting from the trapped charges in the NCs were monitored. EFM can be used to estimate the charging effects affected by the size of the NCs and the injection direction, from the tip or the substrate, by measuring the apparent height difference between NCs. Capacitance spectroscopy and related SCM images show that SCM can be an adequate tool for more detailed analysis of the charging and discharging effects of each NC.

Visualization of MeV ion impacts in Si using scanning capacitance microscopy

Scanning capacitance microscopy (SCM) of $3\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ ${\mathrm{Au}}^{2+}$ ion implanted Si have been performed for doses between $2\ifmmode\times\else\texttimes\fi{}{10}^{8}$ and $5\ifmmode\times\else\texttimes\fi{}{10}^{9}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$. The measurements show a random pattern of reduced SCM signal (charge trapping) correlated with the ion impacts. These features have a lateral dimension of $150--600\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and reveal a pronounced dose dependence. It is argued that the Fermi level near the impacts and along the ion tracks is modified (pinned) due to deep acceptor states formed by the penetrating ions. Substantial evidence for this argument is provided by SCM images obtained at different temperatures, where a strong correlation is revealed between the probing frequency and the emission rate of the single negative acceptor level of divacancy. To the best of our knowledge, this is a direct observation of signatures for individual ion impacts in Si by an electrical scanning technique.

Defects in nitride semiconductors: From nanoscale imaging to macroscopic device behavior

Scanning capacitance microscopy (SCM), atomic force microscopy (AFM), and conductive AFM are used to image the spatial distribution and electronic properties of threading dislocations in Al x Ga 1− x N/GaN epitaxial layers grown by molecular-beam epitaxy. SCM imaging reveals that GaN growth directly on SiC substrates leads to clustering of negatively charged dislocations at nucleation island boundaries, while incorporation of an AlN buffer leads to a random spatial distribution of negatively charged dislocations. Numerical simulations demonstrate that clustered dislocations are less effective in depleting mobile carriers. AFM and conductive AFM imaging reveal the presence of highly conductive threading dislocations which lead to excessive reverse-bias leakage current flow in Schottky diodes. Temperature-dependent current–voltage spectroscopy is used to develop a model for current flow via these dislocations based on a Frenkel–Poole emission process. On the basis of this model, heterostructures are designed to suppress this emission mechanism. Conductive AFM imaging and electrical measurements then confirm the expected suppression of leakage current and specifically of the Frenkel–Poole emission process, demonstrating the validity of both the proposed mechanism of current flow and the approach for leakage current suppression.

Dynamic Measurements of MEMS-Based Field Effect Transistors Using Scanning Capacitance Microscopy

AbstractIn this research, we have employed scanning capacitance microscopy (SCM) to image 2D carrier profiles of a MEMS device. Multiple device states are exercised and examined for changes in carrier response as a function of applied bias. First, experimental and simulated dopant profiles of the source and drain pn junctions were measured with device contacts grounded. Their comparison revealed good agreement. Scanning capacitance microscopy was then used to image changes in carrier distribution within the channel of the device while independent bias voltages were applied to the source, gate, drain, and well regions. Device operation was confirmed by simultaneously measuring the drain current. The SCM image contrast directly beneath the gate was observed to change as a function of applied gate bias voltage.