Scanning-DLTS,EBIC, and CL Investigations of Diamond Indentations in GaAs p+n Junctions

Diamond indentations have been carried out on Zn-diffused GaAs p⁺n junctions on (100) oriented material. Electron-beam induced current (EBIC) investigations revealed the well-known dislocation slip bands in 〈110〉 directions. Scanning deep level transient spectroscopy (SDLTS) imaging proved a deformation-induced point-defect level at E_y + 0.5 eV, which is preferentially concentrated in the dislocation-free regions between the slip bands rather than within the slip bands. Monochromatic cathodolumines-cence (CL) imaging at 10K using different wavelengths revealed only the dislocation-induced recombination activity but not any point-defect luminescence corresponding to the 0.5 eV level found by SDLTS.     

Scanning deep level transient spectroscopy (SDLTS)

Scanning Deep Level Transient Spectroscopy (SDLTS) is a current SEM technique for the detection of the local distribution of deep level centres in semiconductors. It is based on the application of the widely used Deep Level Transient Spectroscopy (DLTS), which enables capacitance changes (or current changes) to be measured in a space charge structure after an excitation pulse as a function of the temperature. This makes it possible to detect the energy levels and the concentration of electronic states in the band gap. By means of scanning DLTS–i.e. the excitation of the levels by an electron probe–deep level states can be investigated with a spatial resolution of a few microns. Scanning the pulsed electron beam (at a temperature selected according to an interesting energy level) yields an SDLTS image. Based on the general principle of the measurement and on the necessary instrumentation the practice of the SDLTS signal generation analysis is presented and experimental examples are discussed.     

Direct assessment of recombination noise in semiconductors using electron beam-induced conductivity

The level of internal noise of the transistors, diodes, and other semiconductor components limits the successful design of any low noise electronic system. All types of noise, namely, Johnson, 1/f, and so forth, are generated due to activity of crystalline defects such as vacancies, dislocations, and others. The intensity of the electron scattering and recombination processes, inflicted by defects (traps), controls the level of noise. Dependent on the dynamic operation condition of semiconductor devices, such as external biases and level of current injection, the traps will generate certain type and level of noise. Material growth or device processing technologies could introduce all kind of defects. Therefore, characterization of the semiconductor wafer in the early stages of processing (at least before packaging) could help to predict the level of noise due to the type and density of defects present on the wafer. Sorting out bad semiconductor chips could save money and effort in the radio frequency design of low-noise circuits. This current study focuses on 1/f noise modeling, which involves most powerful generators of noise and linear defects, named dislocations. The study also examines the possibility of assessing this noise by quantitative electron beam-induced conductivity (EBIC) measurements. These defects could be found in the bulk as well as at the epitaxial interfaces of a semiconductor device. The nanoscale size of these defects makes the scanning electron beam an instrument of choice for the proposed study. Conventional EBIC produces images of the defects, where contrast is proportional to the recombination rate at the site of a defect. Since contrast is measured as a fraction of one percent, the relative nature of contract value precludes quantitative measurements of the recombination rate, thus making quantitative assessment of 1/f noise impossible. In our model, using the Boltzman continuity equation, the recombination-generation processes per unit of length of a dislocation was defined for two operational conditions of EBIC, namely, for low and high intensity of an electron beam. The experimental technique of the quantitative measurement of carrier recombination (Mil'shtein 2001) consists of taking two EBIC scans along the selected defect at two different beam intensities, digitally subtracting the first scan from the second one and normalizing the result to the size of the electron range. The value of the recombination rate, extracted from the model, could then be used to predict the level of 1/f noise in the tested semiconductor sample.     

EBIC and luminescence studies of defects in solar cells

Electron beam-induced current (EBIC) can be used to detect electronic irregularities in solar cells, such as shunts and precipitates, and to perform physical characterization of defects by, e.g. measuring the temperature dependence of their recombination activity. Recently also luminescence methods such as electroluminescence (EL) and photoluminescence (PL) have been shown to provide useful information on crystal defects in solar cells. In this contribution it will be shown that the combined application of EBIC, EL and PL may deliver useful information on the presence and on the physical properties of crystal defects in silicon solar cells. Also pre-breakdown sites in multicrystalline cells can be investigated by reverse-bias EL and by microplasma-type EBIC, in comparison with lock-in thermography investigations.     

Monte Carlo simulation of CL and EBIC contrasts for isolated dislocations

Electron beam-induced current (EBIC) and cathodoluminescence (CL) are widely used to investigate semiconductor materials and devices, particularly to obtain information on the recombination properties and the geometry of defects. This report describes a simple formulation of CL and EBIC contrasts based on the Born approximation of excess carrier density in the presence of a pointlike defect. Quantitative interpretation of the CL and EBIC images is often difficult because of a lack of accurate theory treating simultaneously both the details of the electron beam penetration in the semiconductor and the generation of EBIC and CL signals. To overcome this difficulty, the Monte Carlo approach to the phenomenon of the electron beam penetration in solids has been developed to calculate the CL and EBIC signals during a simulation of the electron trajectory. Results for an inclined dislocation in GaAs are presented.     

Advanced semiconductor diagnosis by multidimensional electron-beam-induced current technique

We present advanced semiconductor diagnosis by using electron-beam-induced current (EBIC) technique. By varying the parameters such as temperature, accelerating voltage (V(acc)), bias voltage, and stressing time, it is possible to extend EBIC application from conventional defect characterization to advanced device diagnosis. As an electron beam can excite a certain volume even beneath the surface passive layer, EBIC can be effectively employed to diagnose complicated devices with hybrid structure. Three topics were selected to demonstrate EBIC applications. First, the recombination activities of grain boundaries and their interaction with Fe impurity in photovoltaic multicrystalline Si (mc-Si) are clarified by temperature-dependent EBIC. Second, the detection of dislocations between strained-Si and SiGe virtual substrate are shown to overcome the limitation of depletion region. Third, the observation of leakage sites in high-k gate dielectric is demonstrated for the characterization of advanced hybrid device structures.     

Application of current-scanning deep level transient spectroscopy to deformed silicon crystals—first results

We have developed a scanning deep level transient spectrometer (SDLTS), using the current-detection principle. With this spectrometer it is possible to detect deep levels in the band gap with a spatial resolution of several μm. From electron-beam-induced DLTS spectra of plastically deformed n-type silicon crystals, one can conclude that under the chosen experimental conditions only minority carrier traps contribute to the SDLTS signal.     

Observation of dislocations and microplasma sites in semiconductors by direct correlations of STEBIC,STEM and ELS

A high voltage electron microscope, equipped with scanning transmission (STEM) attachment, electron beam induced conductivity (EBIC) facilities, and electron energy loss spectrometer (ELS), has been used to investigate semiconductor devices. The capability of STEM to produce, simultaneously or sequentially, conductive and transmission images of the same specimen region, which can also be ELS analysed, is exploited in order to establish direct and unambiguous correlations between EBIC and STEM images of defective regions (dislocations and microplasma sites) in silicon devices. The results obtained are discussed in terms of correlations, resolution, contrast, and radiation damage; in addition, a comparison is made between this method and the other correlation methods based on EBIC/SEM (scanning electron microscope) and TEM (transmission electron microscope).     

The interpretation of EBIC images using Monte Carlo simulations

Charge collection microscopy, usually known by the acronym EBIC (Electron Beam Induced Current) imaging, is a powerful technique for the observation and characterization of semiconductor materials and devices in the scanning electron microscope. Quantitative interpretation of EBIC images is often difficult because of the problem of accurately representing the electron-beam interaction with the semiconductor. This paper uses a Monte Carlo technique to simulate the electron-beam interaction, and it is shown that this permits simple analytical point-source solutions to be generalized to fully represent the experimental situation of an extended, non-uniform, carrier source. The model is demonstrated by application to EBIC imaging in the Schottky barrier geometry.     

A computerized signal acquisition system for the quantitative evaluation of EBIC and CL data in a SEM

Electron beam-induced current (EBIC) and cathodoluminescence (CL) are widely used methods to obtain information about recombination properties of semiconducting materials and their defects on a micrometer length scale. In this article a computerized SEM (scanning electron microscope) setup is described, which enables us to perform simultaneous measurements of several signals and automatic temperature-dependent measurements. As examples for the performance of this system we present results obtained by simultaneous EBIC/CL experiments, allowing a reconstruction of the defect geometry. In a second example, the temperature dependence of the EBIC contrast is analyzed, introducing the method of EBIC spectroscopy.     

Development of fast-response portable NDIR analyzer using semiconductor devices

In this paper, a novel fast response NDIR analyzer (FRNDIR), which uses an electrically pulsed semiconductor emitter and dual type PbSe detector for the PPM-level detection of carbon dioxide (CO₂) at a wavelength of 4.28 μm, is described. Modulation of conventional NDIR energy typically occurs at 1 to 20 Hz. To achieve real time highspeed measurement, the new analyzer employs a semiconductor light emitter that can be modulated by electrical chopping. Updated measurements are obtained every one millisecond. The detector has two independent lead selenide (PbSe) with IR band pass filters. Both the emitter accuracy and the detector sensitivity are increased by thermoelectric cooling of up to —20 degrees C in all semiconductor devices. Here we report the use of semiconductor devices to achieve improved performance such that these devices have potential application to CO₂ gas measurement and, in particular, the measurement of fast response CO₂ concentration at millisecond level.     

Electron Microscope Studies Of Vpe Gainas Layer Structures Suitable For Use As Infrared Leds

Electron microscope investigations have been carried out on vapour grown (100) GaAs/GaInAs structures designed for use as infrared emitters of wavelength 1·06 μm. The structures consist of a GaAs substrate, a graded layer in which the indium concentration is increased from zero to 17 atomic %, and a constant composition Ga_0·83In_0·17As layer which contains a p-n junction. X-ray microprobe analysis of cross-sections of the slices established the uniformity of the grading. TEM analysis showed a dense and extensive asymmetric network of misfit dislocations (1 × 10¹² m^?2 (10⁸ cm^?2)) in the graded layer, threading dislocations and other anomalous contrast features extending from the graded layer through the p-n junction to the surface (local densities of 1 × 10¹¹–1 × 10¹² m^?2 (10⁷–10⁸ cm^?2)), and a planar network of dislocations just below the surface (spacing 0·2–2 μm). SEM EBIC and CL studies of the layer above the junction revealed dark spots, and a cross-grid of dark lines, which could be correlated with the threading defects, and the dislocation network just below the surface, respectively. The SEM results showed that these defects had a deleterious effect on the luminescent and electrical properties of the material in the vicinity of the p-n junction, and would therefore impair the performance of devices made from these layer structures.     

A hybrid defect detection for in-tray semiconductor chip

The requirements for high-speed and high-precision defect inspection in semiconductor chip are growing rapidly because of the complicated surface in semiconductor chip. Due to manufacturing tolerance of IC tray, the misalignment from the chip positioning shift and rotation are always presented for the application of in-tray inspection. In the beginning, this paper focuses on compensating the positioning shift and rotation of in-tray chip by using the proposed image alignment algorithm before the defect detection. After applying the process of image alignment, a hybrid approach of defect detection is applied to detect the defects of in-tray chip. Furthermore, this hybrid approach simultaneously detects the defects based on its surface by the following two categories: (1) the complicated surface in the circuit and (2) the primitive surface on the bump. As mentioned above, the image alignment strategy and the adaptive image difference method are applied in the detection of complicated surface, and the design-rule strategy is adapted to detect the defects on bumps. Finally, the experimental results show that the proposed image alignment strategy and hybrid approach can accurately and rapidly inspect the defects of in-tray chip. This approach is superior to the traditional template matching in defect detection. In addition, the computational complexity can be efficiently reduced by the proposed hybrid strategy.     

SEM and TEM studies of defects in Si-doped GaAs substrate material before and after Zn diffusion

Si-doped GaAs slices after Zn diffusion exhibited a marked decrease in luminous efficiency and a large increase in p-n junction depth when the initial carrier concentration due to the Si was > 3·5 times 10²⁴ m^?3. SEM studies using the CL and EBIC methods, and TEM examinations using plan-view and cross-section specimens, showed that these behaviours were associated with high densities of structural defects, interpreted as Zn precipitation. Reasons for these behaviours in terms of nucleation behaviour and diffusion mechanisms are suggested.     

Ion damage to the specimen in the SEM studied by the EBIC technique

This paper reports ion damage to Si and GaAs diodes during examination in the SEM as revealed by the electron beam induced conductivity (EBIC) technique. Also reported here is the emission of energetic negative ions having a mass-to-charge ratio of 32 from the lanthanum hexaboride electron gun. It is believed that these ions are (O₂)^?, although the possibility that they might be S^? cannot be ruled out. These ions give rise to damaged regions of the specimen which are circular in shape and which have a diameter related to that of the beam-limiting aperture in the SEM final lens. It is presumed that this problem can be avoided, if necessary, by the use of an ion trap at some point in the electron column.     

High-resolution scanning near-field EBIC microscopy: application to the characterisation of a shallow ion implanted p+-n silicon junction

High-resolution electron beam induced current (EBIC) analyses were carried out on a shallow ion implanted p⁺–n silicon junction in a scanning electron microscope (SEM) and a scanning probe microscope (SPM) hybrid system. With this scanning near-field EBIC microscope, a sample can be conventionally imaged by SEM, its local topography investigated by SPM and high-resolution EBIC image simultaneously obtained. It is shown that the EBIC imaging capabilities of this combined instrument allows the study of p–n junctions with a resolution of about 20 nm.     

Scanning electron microscopy studies of double-layer silicon structures prepar by epitaxy and direct bonding

The electrical properties of multilayer structures obtained by direct bonding of silicon wafers and epitaxial growth have been investigated. The measurements were made by scanning electron microscopy (SEM) in either secondary electron or electron beam-induced current (EBIC) regime, using cross sections of the structures with a p-n junction formed in the subsurface region of the active layer. The measurements of defect recombination activity were made using Schottky diodes formed on the active layer surfaces. Parasitic p-n junctions in some samples under a small direct voltage have been observed and the reason for the appearance of such parasitic junctions has been established. Two types of defects with different distribution densities and amplitudes of EBIC contrast have been detected.     

EBIC microscopy of double-heterostructure laser materials and devices

The electron beam induced current (EBIC) mode of the scanning electron microscope (SEM) has been used to characterize double heterostructure laser materials and devices in GaAs/Ga_1–xAl_xAs. Scanning the electron probe across the cleaved face of the laser structure shows that displacement of the p-n junction with respect to the heterojunctions is not uncommon with displacements ～ 1 μm occurring. Concurrent measurement of the minority carrier diffusion length gives very short lengths of 0·3–0·4 μm, differing from those in much thicker layers. Scanning the electron probe in the contact plane indicates clearly that long-lived lasers exhibit marked heterogeneity during degradation. Considerable complexity and variation is recorded depending upon the fabrication details and degradation conditions adopted.     

Observation of current-density filamentation in multilayer structures by EBIC measurements

The total current-voltage characteristics of the p⁺-n⁺-p-n^? and n⁺-p-n-p^? diodes under investigation show branches of negative differential resistance. Accompanied by the appearance of negative differential resistance is a filamentation of current-density and electric-field distribution. Electron beam-induced current (EBIC) measurements were used to examine the properties of filamentation from the point of view of self-organized pattern formation. Besides the detection of the spatial distribution of the electric field, EBIC measurements give information on current-density filamentation. Furthermore, the perturbation by the electron beam gives information on the dynamic behavior of the filamentary structure.     

Using microscopic techniques to reveal the mechanism of anion exchange in crystalline co-ordination polymers

Co‐ordination polymers are currently attracting extensive interest due to their potential applications as supramolecular hosts, vessels, and frameworks for storage and separations. Many applications rely on the ion exchange capabilities of these compounds, and considerable debate surrounds the mechanism by which ion exchange occurs in co‐ordination polymers. Here AFM and SEM were applied, for the first time, to investigate this class of materials. In situ AFM studies revealed the mechanism by which anion exchange and the subsequent structural transformations of the crystalline co‐ordination polymers {[Ag(4,4′‐bipy)]BF₄}_∞ and {[Ag(4,4′‐bipy)]NO₃}_∞ occur. The process is initiated by the dissolution of the metastable crystalline polymer, followed by the subsequent crystallization of the new stable phase on the surface of the original crystal. The formation of deep clefts in the metastable polymer crystal during the transformation allows the solution to access the successive crystalline layers. Thus, the entire process can be viewed as a self‐perpetuating cascade of dissolution and recrystallization throughout the macroscopic crystal. SEM data consolidate the findings of AFM. These techniques collectively illustrate that the anion exchange, and subsequent structural transformation, proceeds via a solvent‐mediated mechanism, rather than a purely solid‐state one.