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In this work, the influence of the tip-geometry and an unusual low frequency behavior in scanning capacitance microscopy is investigated experimentally and theoretically on metal–oxide–semiconductor (MOS) and Schottky type junctions on gallium–arsenide (GaAs). Using a two-dimensional model we find that on Schottky type junctions the electric field around the tip is screened by the surface states and that the essential parameters entering the capacitance versus voltage C(V) characteristics are the doping level and the contact area only. On a MOS-type junction, the electric field from the tip penetrates into the semiconductor and the tip geometry effects are much larger. C(V) spectra are fitted to the experimental data and allowed a quantitative determination of doping levels, oxide thickness, and contact area without moreover calibration measurements. Furthermore, we show that the natural surface depletion field on GaAs generates a permanent minority carrier accumulation around the tip–apex. In contrast to thermally generated minority carriers in the space charge region of a large area device, the minority carrier distribution around the SCM tip–apex is detected up to much higher excitation frequencies. An analytic approach to estimate the transition frequency between the low and high frequency regime is also given.

In this work, we present a scheme for room temperature detection of single subsurface InAs quantum dots buried in GaAs by Atomic Force Microscopy based local photocurrent spectroscopy. The measurements were performed at room temperature and ambient conditions. The AFM was used as a nanopositioning system and the AFM tip was used to create a nano-scale Schottky contact in the vicinity of a QD. The photocurrent spectra clearly showed peaks from quantum dots located in the vicinity of the AFM tip. The spatial resolution of the method was determined to be in between 100 nm and 1000 nm. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work, photocurrent images of lithographically processed GaAs/AlAs heterostructures are recorded by an atomic force microscope. It is found that the AFM tip sample contact is strongly dependent on the thickness of the native oxide layer on the sample surface. Therefore, the photocurrents increase if a successively increasing tip sample force is applied, which leads to a gradual penetration of the surface oxide layer. Due to the complex behavior of the photocurrent as a function of tip-bias and tip-force, the contrast in photocurrent images is non-monotonic and can be reversed under appropriate bias and force conditions.

Photocurrent (PC) spectroscopy is employed to study the carrier escape from self-assembled InAs/GaAs quantum dots (QDs) embedded in a Schottky photodiode structure. As a function of the applied field, we detect a shift of the exciton ground-state transition due to the quantum-confined Stark effect ( S = 4.3 meV / V ). The tunneling time, which is directly related to the observed photocurrent linewidth due to τ ∼ ℏ / ( 2 Γ ) , changes by a factor of five in the photocurrent regime. The measured linewidth dependency on the electric field is modeled by a simple 1D WKB approximation for the tunneling process, which shows that the energetic position of the wetting layer is important for the measured tunneling time out of the dot. In addition to that we present cross-sectional atomic force measurements (AFM) of the investigated photodiode structure. The method needs a minimum of time and sample preparation (cleaving and etching) to obtain the dot density, dot distribution, and give an estimate of the dot dimensions. Etching only the cleaved surface of the sample opens up the opportunity to determine the properties of a buried dot layer before or even after device fabrication.

The fabrication of nanostructured dielectrics of high purity produced by electron beam induced deposition (EBID) was investigated. Additionally, the process parameters were optimized towards high deposition rate. Silicon oxide was chosen as exemplary dielectric. The deposition was performed with an electron microscope with a self-designed nozzle system. An organo-silicon precursor was used to deposit silicon oxide. The increase of the oxygen content and the reduction of carbon contaminations of the depositions were preformed by adding molecular oxygen. Patterns of large areas as well as nm-scale arrays were fabricated. To optimize the deposition rate the correlation between beam parameters and deposition rate was studied. It has been shown that this direct-write method allows obtaining arbitrary structures with superior material quality.

In this article we report the straggling of long-range implantation damage in silicon in the forefront of a focused ion beam induced amorphization zone. Irradiation was carried out at room temperature at a current density of 0.75 A cm−2 (5×1018 ions/cm2 s) using 50 keV Ga+ ions. A highly sensitive tool for detection, an n-metal–oxide–semiconductor field effect transistor is used to quantify and to characterize the distribution profile of ion beam induced electroactive defects. Scanning the beam over active devices allows the extraction of a three-dimensional profile of defects. In situ monitoring of the drive current and intermitting charge pumping measurements revealed the progressive nature of the damage, the generation of interface states, and the lateral extension of irradiation related defects. Far reaching damage cascades extend at least 300 nm in the beam direction and about 220 nm perpendicular to the beam direction of the substrate and define the region of electrically active defects due to parti...

In this article we explore the application of scanning capacitance microscopy (SCM) for studying focused ion beam (FIB) induced damage in silicon. We qualitatively determine the technologically important beam shape by measuring the SCM image of FIB processed implantation spots and by comparison of topographical and SCM data. Further, we investigate the question how deep impinging ions generate measurable damage below the silicon surface. For this purpose, trenches were manufactured using FIB and analyzed by SCM in cross-sectional geometry.

This paper presents a novel technology of lateral profile engineering addressing nonuniform-channel MOS devices. For the first time MOS devices with highly nonuniform 2-D doping profiles are achieved by post-processing implantation of channel doping peaks. By reducing the thermal budget to a single anneal/activation step, any unintentional broadening or washout of the doping profiles is avoided. We demonstrate the feasibility of this scheme in terms of trap generation and damage, and the appropriateness of this approach to explore nonuniform-channel MOS devices. As predicted by simulations, the Ion/Ioff ratio of MOS devices is greatly improved by the introduction of peaking channel dopings. These devices are much less prone to hot-carrier degradation due to reduced electric fields, are less affected by drain induced barrier lowering (DIBL) and exhibit improved resistance to punch through, thus being easier to scale into the ultra-deep-submicron regime.

In this paper we explore the application of scanning capacitance microscopy (SCM) for studying focussed ion beam (FIB) induced damage in silicon. We qualitatively determine the technologically important beam shape by measuring the SCM image of FIB processed implantation spots, and by comparison of topographical and SCM data. Further, we investigate how deep impinging ions generate measurable damage below the silicon surface. For this purpose, trenches were manufactured using FIB and analysed by SCM in cross-sectional geometry.

In this article, we explore the properties of ZrO2 as dielectric material for scanning capacitance microscopy (SCM). The ZrO2 layers were grown by chemical vapor deposition (CVD) at T=450 °C. The low growth temperature together with the good reproducibility of the CVD process and the high dielectric constant make ZrO2 a very promising material for SCM applications. Compared with SiO2 as dielectric material, much thicker ZrO2 layers can be used resulting in reduced leakage currents and improved signal quality. For SiO2 and ZrO2 layers having the same thickness, the latter yields higher signals and therefore an enhanced sensitivity. Furthermore, ZrO2 was found to be quite insensitive to parasitic charging effects, which often disturb SCM measurements on samples with SiO2 layers.

We present photocurrent images and spectroscopic results of sub-surface InAs quantum dots (QDs) and thin films of colloidal PbS QDs obtained at room temperature and under ambient conditions by means of photoconductive atomic force microscopy (pcAFM) under 916 nm and 900 nm illumination respectively. InAs QDs appear as dark areas in the photocurrent image, because imaging was performed at the wetting layer excitation energy. The PbS nanocrystal film imaged at the energy of the first excitonic transition displays local variations of the photoactivity. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work, an atomic force microscope (AFM) with conductive tip was applied to investigate the local photoconductive behavior of lithographically processed GaAs/AlAs heterostructures. Photocurrent images and current vs. voltage (IV) curves were recorded under different tip-sample voltage and tip force conditions. It is found that the AFM tip-sample contact is strongly dependent on the thickness of the native oxide layer on the sample surface. Therefore, the photocurrents increase if a successively increasing tip-sample force is applied, which leads to a gradual penetration of the surface oxide layer. The force dependence of the Schottky barrier height was applied to build a laser free AFM feedback for photocurrent spectroscopy. This feedback system was used to record photocurrent vs. wavelength spectra at a constant tip-sample force.

In this paper we compare macroscopic C-V-measurements with (local) scanning capacitance (SCM) measurements to extract electrical parameters. In future microelectronic CMOS devices, [email protected] dielectrics, primarily as gate oxides, will play an important role. The characterization of their electrical behaviour is one key issue to evaluate their suitability. We deposited zirconium dioxide (ZrO"2) thin films by metal-organic chemical vapor deposition (MOCVD) on (100)-silicon substrates to fabricate metal oxide semiconductor gate stacks. These devices were evaluated by conventional C(V) characterization using a probing station. Additionally, we applied a new C(V)-characterization method, allowing to determine electrical characteristics of nm-thick dielectric films on a nanoscopic scale. This method enabled us to directly compare the nanoscopic and macroscopic measurements. As a result, local and global measurements turned out to be consistent. A comparison of our ZrO"[email protected] layers with thermal SiO"2 films indicate a superior behaviour of MOCVD grown ZrsO"2 film.

We have studied the evolution of the GaAs, InAs and GaSb surfaces due to FIB exposure. In contrast to conventional bottom up or top down processes the observed nanopattern formation is discussed, based on a subtractive self-organization process relying on material decomposition induced by FIB exposure.

In this work, a setup for quantitative scanning capacitance spectroscopy is introduced, where an ultrahigh precision, calibrated capacitance bridge is used together with a commercially available atomic force microscope (AFM). We show that capacitance data measured with this setup are of comparable quality as data obtained on macroscopic metal oxide semiconductor capacitors. In addition, our setup is sensitive enough to resolve the energy distribution of interface traps with the spatial resolution of an AFM. This is an advantage compared to conventional scanning capacitance microscopes, which have a limited energy resolution and only yield qualitative results due to large modulation voltages.

It is shown that surface roughness becomes increasingly important as oxide thicknesses decrease. Silicon-silicon dioxide capacitances with thicknesses of 7 nm, 15 nm, and 50 nm are measured with an atomic force microscope (AFM). The height data thusly obtained is used to create three dimensional simulation structures to reproduce measurement data obtained from leakage current measurements. The leakage currents are simulated using the Fowler-Nordheim (FN) tunnelling current model

There is an increasing interest in cell-based microelectronic biosensors for high-throughput screening of new products from the biotech pipeline. This requires fundamental knowledge of the biocompatibility of the materials used as the growing support for the cells. Using monolayer-forming Caco-2 cells of human origin, the biocompatibility of silicon wafers coated with various metals, dielectrics and semiconductors was assessed. Besides microscopic inspection, proliferation of cells indicating viability as well as brush border enzyme activity indicating differentiation of adherent growing cells were chosen as parameters to estimate biocompatibility. The type of wafer used for deposition of the coating initially influences the biocompatibility of the final product. Whereas p-doped silicon was fully biocompatible, n-doped silicon reduced the proliferation of cells. Among the different coatings, Al and Ti even increased the cell growth as compared to glass. Culturing the cells for 6 days on coated wafers demonstrated that the differentiation of adhering cells on Ti- and ZrO2-coated wafers was comparable to glass, whereas coatings with Si3N4, Au, Al, and ITO reduced differentiation to 15–35%. In the cases of Au and Si3N4 this effect equilibrated with prolonged culturing. These results demonstrate the importance of a careful selection of the materials used for the production of cell-based biosensors.

In our previous work we showed that a reproducible monotonic relation between Scanning Capacitance Microscopy (SCM) signal and the sample doping is obtained under appropriate SCM operating conditions. In this work, we quantitatively determine the two‐dimensional carrier distribution of an n‐type ion‐implanted collector region of an industrial transistor sample. As the structures were large enough so that tip geometry effects could be neglected, the SCM data were converted into a two‐dimensional doping distribution via a simple lookup table, which was generated from a one‐dimensional doping profile measured on a reference wafer. In case the depth distribution of carriers is unknown, we show that the lookup table can also be calculated and a calibration can be carried out using e.g. the substrate doping as reference point.

Focused ion beam (FIB) systems are widely used for device modifications during the design debugging phase of integrated circuits (IC's) development. Nevertheless, it appears necessary to further understand the interaction between the finely focused ion beam and IC's to assure that these modifications do neither induce electrostatic discharge of the devices nor degradation due to FIB irradiation induced damage. The purpose of this study is to analyze the focused ion beam interaction with n-MOSFET devices addressing irradiation damage related device degradation apart from charging effects. For the first time, monitoring of device parameters during ion beam exposure enables us to quantify the progressive nature of device degradation. By in-situ electrical sensing of the devices during focused ion beam exposure, the impact on device parameters (I/sub Dsat/, I/sub Off/, and mobility) is studied. The FIB exposed devices exhibit no damage related degradation as long as the milling is out of the reach of the active channel. Progressive degradation starts when long-range damage cascades extend into the channel region. The related damage can be attributed to mobility decrease in the channel region and is quantified by a semi-empirical mobility model. As a result we present an experimental setup that prevents ESD induced device degradation and allows the investigation of damage related device degradation. In combination with a moderate annealing process that mitigated FIB induced irradiation damage this enables successful modification of MOSFET devices even in the front end regime.

Application of focused ion beams (FIB) to circuit modification during design and debugging of integrated circuits is limited by the degradation of active devices due to beam induced crystal damage. In order to investigate FIB induced damage formation theoretically, we have extended our 1-D/2-D binary collision (BC) code IMSIL to allow surface movement due to sputtering. In contrast to other dynamic BC codes, the crystal structure of the target and damage generation during implantation may be taken into account. Using this tool we simulate the milling of trenches in the gate stack of MOSFETs and compare the results with transmission electron microscopy cross sections and charge pumping data. The simulations confirm that damage tails are generated that are a factor of two deeper at relevant defect concentrations than expected by conventional BC simulations. This result is shown to be due to recoil channeling in spite of the fact that a beam-induced surface amorphous layer is present throughout the implant. In addition, we discuss the accuracy of the experimental results and the simulations.

The focused ion beam has been acknowledged as a versatile tool for local sputtering as well as local deposition of material. A beam diameter below 10 nm is feasible and renders FIB a powerful tool for microstructure fabrication and generation. This experimental study investigates the geometrical limitations of FIB processing as well as the implications on the processed material. The high energetic ions of the primary beam also change the properties of the processed material due to implantation and atomic mixing. The incorporation of Ga from the FIB may be beneficial in the case of deliberate implantation or unfavorable as a chemical impurity. Higher doses of ion irradiation caused amorphisation of the material. The effects of FIB processing on the substrates as well as deposited structures are illustrated.

For the first time we demonstrate the capability of focused ion beams for engineering in the front end regime. We have shown that by a robust protection for MOSFET, Focused ion beam induced ESD degradation can be avoided and implantation induced damage could be well controlled and mitigated by a moderate RTA process. By a masked through gate implantation technique followed by a moderate annealing/activation process we have exemplarily modified the threshold voltage of test transistors on fully featured wafers whereby any unintentional change of devices nearby could be avoided.

Mixed films of PbS quantum dots and fullerene derivatives were investigated using spectrally resolved photoconductive atomic force microscopy (pcAFM) equipped with an external source measure unit to accurately measure small currents. Combining pcAFM with a tuneable laser light source allowed us to record local internal power conversion efficiency (IPCE) spectra and thus to determine the wavelength of highest photoactivity. Samples exhibited photoactivity in the near infrared around 900 nm with an IPCE of 10% at a single measurement point. Photocurrent images with a 5 nm pixel size were recorded showing inhomogeneous photocurrent distribution uncorrelated to the topography but reflecting the heterogeneous make-up of the film. The perpetual degradation of the photocurrent due to sample oxidation under ambient conditions was also monitored.

In this work, photocurrent (PC) spectra on GaAs measured by conductive atomic force microscope (AFM) tips are analyzed quantitatively. The measurements were carried out on n-doped bulk GaAs samples as a function of excitation wavelength and tip bias. The measured data are compared to simulations employing a two-dimensional self consistent POISSON SOLVER. It is found that the shape of the depletion zone below the AFM tip is strongly influenced by the tip bias and the surface potential, which leads to a clear difference between PC data obtained with large area devices and conductive AFM tips.

Conductive atomic force microscopy in combination with an optical setup is a useful tool for obtaining spectrally and spatially resolved photocurrent information on photoactive nanostructures. We have demonstrated photocurrent mapping under ambient conditions using sub-surface InAs quantum dots (QDs) as an example, whereby the QDs appear as dark areas in the photocurrent signal. Spectrally resolved measurements of on-dot and off-dot areas show distinct differences, confirming the existence of QDs at the detected position.

In this work, an unusual low frequency behavior observed in scanning capacitance microscopy/spectroscopy on GaAs/Al2O3 junctions is investigated. Using a two-dimensional simulation, we show that the frequency behavior of the capacitance—voltage curves can be explained through an increased minority carrier concentration at to the GaAs–Al2O3 interface and tip geometry effects on the nanoscale. An analytic approach to estimate the transition frequency between the low frequency and high frequency regime is also given.

In this letter, confocal optical microscopy is used to investigate the intensity patterns of an infrared vertical cavity surface emitting laser in three dimensions with high spectral resolution. The measurements were performed between the near field (Fresnel) regime and the far field (Fraunhofer) regime. The calculated intensity patterns were found to be in good agreement with the measured intensity distribution. The calculations together with the measurements can be used to determine the phase relation between different positions inside the gain medium.

In this work, the influence of the tip geometry in scanning capacitance microscopy is investigated experimentally and theoretically on metal-oxide-semiconductor- (MOS) and Schottky-type junctions on gallium-arsenide (GaAs). Using a two-dimensional model we find that on Schottky-type junctions the electric field around the tip is screened by the surface states and that the essential parameters entering the capacitance versus voltage C(V) characteristics are the doping level and the contact area only. In contrast to that, the electric field from the tip penetrates into the semiconductor on a MOS-type junction, and the tip geometry effects are much larger. C(V) spectra are fitted to the experimental data and allowed a quantitative determination of doping levels, oxide thickness, and contact area without further calibration measurements.

Quantitative scanning capacitance microscopy on InAs quantum dots requires low modulation frequencies and complete darkness. Using a modified feedback method on our atomic force microscope, which allows to switch off the laser temporarily while the feedback loop keeps running, images of buried InAs self assembled quantum dots were acquired. The dots are clearly visible as bright areas in a contrast-rich capacitance landscape, which we attribute to thickness variations of the InAs wetting layer. Even at room temperature, spectroscopic data recorded at on-dot and off-dot positions exhibit a completely different behavior and show evidence of quantized states inside the dots.

Scanning capacitance microscopy (SCM) is known to be a valuable tool for carrier mapping and profiling on nanoscale semiconductor samples. Certain applications, however, such as quantitative capacitance microscopy on InAs quantum dots, e.g. require low modulation frequencies and complete darkness, which are requirements completely incompatible with the current commercial SCM systems relying on a laser feedback system. For this reason, an intercepted feedback method was developed, which allows to switch off the laser temporarily while the feedback loop keeps running. As an application, images of sub surface InAs self assembled quantum dots were recorded. The InAs dots are clearly visible as bright areas in a contrast-rich capacitance landscape, which we attribute to local thickness variations of the InAs wetting layer in our sample.

In most atomic force microscopes (AFMs), the motion of the tip is detected by the deflection of a laser beam shining onto the cantilever. AFM applications such as scanning capacitance spectroscopy or photocurrent spectroscopy, however, are severely disturbed by the intense stray light of the AFM laser. For this reason, an intercepted feedback method was developed, which allows to switch off the laser temporarily while the feedback loop keeps running. The versatility of this feedback method is demonstrated by measuring tip-force dependent Schottky barrier heights on GaAs samples.

In this work, we introduce a two color, low intensity photocurrent feedback method for photocurrent spectroscopy utilizing an atomic force microscope (AFM). In most applications, measurements with weak optical excitations are not feasible with an AFM because the powerful AFM feedback laser severely disturbs the measurements. Therefore, we have developed a feedback system based on the pressure dependent Schottky barrier height at the tip-sample interface. The versatility of the new feedback system is demonstrated by recording high resolution photocurrent spectra on GaAsInAs heterostructures.

The quality of electron-beam deposited, few nanometers thick, SiO2 layers on silicon substrates was investigated by scanning capacitance microscopy and spectroscopy. Rapid thermal annealing had to be applied prior to the capacitance versus voltage [C(V)] measurements to obtain typical metal-oxide-semiconductor behavior, and it was found that the total oxide charge is negative on the deposited oxide layers. Higher annealing temperatures resulted in an overall reduction of the number of oxide charges. This opens up the possibility to use electron-beam deposited SiO2 as a dielectric material in metal-oxide-semiconductor prototyping applications.

We present cross-sectional atomic-force-microscope measurements of buried self-assembled quantum dots. The used method needs a minimum of time and sample preparation (cleaving and etching) to obtain the dot density, dot distribution, and give an estimate of the dot dimensions. Etching only the cleaved surface of the sample opens up the opportunity to determine the properties of a buried dot layer before or even after device fabrication.

We investigate the growth of InAs quantum dots on patterned GaAs substrates. The GaAs substrate has been structured using holographic lithography. Quantum dot formation along the patterns has been observed as well as an increase in homogeneity of the quantum dots. Furthermore, the use of ion beams focused to nanometer diameters for substrate patterning has been studied and showed promising results. For the investigation of vertically aligned InAs quantum dots, cross-sectional atomic force microscopy has been successfully employed.