Determination of trace elements in a silicon single crystal

Instrumental neutron activation analysis was applied to the determination of trace impurity elements in a silicon single crystal. Impurity concentrations in polysilicon melt were compared with those in a single crystal. Impurity concentrations in artificial quartz were also compared with those in natural quartz. Segregation coefficients in Au, Ir and Sb were determined at different concentrations. The segregation coefficient of an element in a silicon single crystal is constant over a critical concentration, it becomes larger gradually under the critical one, and at last it becomes larger than 1.     

Effect of transition element doping on crystal structure of rare earth borosilicides REB44Si2

On a previous study on samples of doped-YB₄₄Si₂, an improvement of thermoelectric properties has been achieved. Regarding the interesting effect of the doping of transition elements on the thermoelectric properties, a single crystal study has been carried out on Zn doped, Rh doped and Ni doped samples to assess how the transition element doping affects the crystal structure. Refinements were carried out based on the structural model solution of YB₄₄Si₂ reported in a previous study. Variations in the silicon contents were found in the doped single crystals. Splitting of partially occupied sites has also been detected for some of the doped samples. In this paper we present differences in the partial occupations of boron and silicon sites. Possibility of transition elements insertions based on the differences in crystal structures will be presented.     

Uses of PGAA at the Dalat reactor

A facility for neutron capture prompt -ray spectroscopy for activation analysis has been intstalled at the tangential beam tube of the 500 kW Dalat reactor. Using a single crystal of silicon for filtering the thermal neutron beam and the 73 cm³ HP-G detector shielded by common materials with flexible configurations suitable to various samples, LOD of nearly 30 elements were estimated. Applications of PGAA in the determination of elemental concentrations in biological, environmental, geological and industrial product samples are presented.     

Spark-source mass spectrometric assessment of silicon concentrations in silicon-doped gallium arsenide single crystals

The spark-source mass spectrometric assessment of silicon concentrations in silicon-doped vertical-gradient-freeze gallium arsenide is presented. The silicon concentrations determined are compared with the charge-carrier densities measured by means of the Hall effect with van der Pauw symmetry along the axis of a single crystal.     

Photovoltaic substrates and hafnium based gate dielectrics characterized with total reflection X-ray fluorescence

In this study, the capabilities of total reflection X-ray fluorescence spectroscopy characterization for both the photovoltaic industry and advanced semiconductor processing were investigated. Analysis of single crystal silicon coupon samples from various cleans during photovoltaic processing showed that certain clean steps were more effective in removing trace metal contamination. The multicrystalline photovoltaic silicon sample also had detected, but difficult to quantify, metallic contamination. Changes in the silicon dioxide content of hafnium silicate films used in semiconductor processing were also characterized by total reflection X-ray fluorescence spectroscopy analysis.     

Effect of Nb,Ti, and W ion implantation on surface properties and cell compatibility of silicon carbide

Silicon carbide is considered as a bio-inert semiconductor material; consequently, it has been proposed for potential applications in human body implantation. In this study, we study the effect of implanting different metal ions on the surface properties of silicon carbide single crystal. The valence states of the elements and the surface roughness of implanted SiC were studied using X-ray photoelectron spectroscopy and atomic force microscope, respectively. Osteoblastic MG-63 cells were utilized to characterize the cytocompatibility of ion implanted SiC. The results show that after Nb ion implantation on the SiC surface, it mainly exists in the form of Nb–C bond, Nb–O bond, and a small amount of metallic niobium. The titanium implanted on SiC primarily forms Ti-C bond and Ti-O bond. The tungsten implanted on SiC mostly presents as metallic tungsten and W–O bond. The roughness of silicon carbide single crystal is improved by ion implantation of all three metal ions. Ion implantation of titanium and niobium can improve the cell compatibility and hydrophilicity of silicon carbide, whereas ion implantation of tungsten reduces the cell compatibility and hydrophilicity of silicon carbide.     

Determination of impurities in semiconductor grade silicon by instrumental neutron activation analysis

Instrumental neutron activation analysis has been applied to semiconductor grade silicon to study the concentration levels of impurity elements, the contamination during the single crystal growing process, and the vertical and radial distributions of impurities, along with the decontamination effect in the analysis. Twenty elements of Au, Br, As, W, Cr, Co, Na, Eu, La, Se, Zn, U, Th, Hf, Fe, Sb, Ag, Ce, Tb and Ta have been analyzed in p- and n-type wafers, single crystals and a polycrystal by a single comparator method using two comparators of gold and cobalt. Considerable surface contamination has been found and could be removed by etching the surface with nitric and hydrofluoric acid before and after irradiation. The impurity concentration has been found to be generally increased in the process of single crystal growth. The vertical and radial distributions of impurities have revealed that some impurity elements were more concentrated in the top region of a single crystal rod than in the middle region, and that Br, Cr, La, Eu and Sb were enriched in the central region and As, U and Fe in the outer region.     

Mechanism of the emergence of the photo-EMF upon silicon liquid crystal–single crystal contact

The effect light has on a silicon liquid crystal–single crystal contact at different temperatures of the surface doping of silicon, and when BaTiO₃ nanoparticles are added to the composition of a liquid crystal, is studied. The mechanism of the emergence of the photo-EMF in the liquid crystal–silicon structure is explained.

     

Limitations and improvements of trace element analysis with proton-induced X-rays

The technique of trace element analysis by the detection of characteristic X-rays induced by high energy proton bombardment is critically examined. A discussion of the restrictions imposed by detector resolution is made, the behavior of the cross-section for X-ray production as a function of energy and atomic number is discussed. The effect of this behavior upon analysis time is demonstrated. Background is discussed in terms of its effect on the total counting rate. The use of a silicon solid state detector to determine the overlappingK-lines of light elements andL-lines of heavy elements is shown to have severe limitations. A combination of crystal monochromators and solid state detectors is suggested as a means to circumvent some of the fundamental limitations encountered with a single detector. An experimental arrangement for the use of twenty-four crystal monochromators and two solid state detectors is shown. Work supported in part by the U.S. Atomic Energy Commission.     

混合酸制备四氟化硅气体用于硅同位素测量

1引言在自然界中,硅元素有3种稳定同位素28Si,29Si和30Si,丰度分别为92.23%,3.68%和3.09%。准确测量硅的摩尔质量,需准确测量硅的3种同位素的丰度值。目前,测量硅摩尔质量最佳的方法是采用SiF4气体测定硅同位素的丰度值,这     

Antireflective sol–gel TiO2 thin films for single crystal silicon and textured polycrystal silicon

In this paper, antireflective TiO₂ thin films have been prepared on single crystal silicon, and textured polycrystal silicon by sol–gel route using the dip-coating technique. The thickness and the refractive index of the films have been optimised to obtain low reflexion in the visible region, by controlling both the concentration of the titanium isopropoxide (Ti(ⁱOPr)₄), and the annealing temperature. We showed that the use of a TiO₂ single layer with a thickness of 64.5 nm, heat-treated at 450 or 300 °C, reduces the reflection on single crystal silicon at a level lower than 3% over the broadband spectral ranges 670–830 nm and 790–1010 nm, respectively. In order to broaden the spectral minimum reflectance as much as possible, we have proposed to texture polycrystal silicon wafers, and to coat these wafers by a TiO₂ single layer with a thickness of 73.4 nm. In this case, the reflectance has been reduced from 27 to 13% in the spectral range 460–1000 nm.     

Surface orientation characterisation of rough mc‐silicon surfaces by confocal microscopy and EBSD

For many semiconductor and photovoltaic applications the quality of substrate surfaces is an important requirement for the development of new devices. Therefore, methods are needed to analyse the surface structure in detail. In the following a new method is described that allows a fast analysis of as‐cut or artificially modified and textured surfaces. It uses laser confocal microscopy images. Therefrom the orientation of small surface elements are detected and depicted in an orientation distribution function of surface normals. The method is applied to as‐sawn mc‐silicon surfaces. It will be shown that it is also possible to determine the grain orientation for grains near 〈111〉 crystal direction by this method. The combination of electron backscatter diffraction and orientation distribution function analysis enables the detailed investigation of surface elements of an anisotropic etched silicon wafer. Inhomogeneity of surface textures can easily and rapidly be visualised by this method. Copyright © 2012 John Wiley & Sons, Ltd.     

Summary of ISO/TC 201 Standard: X ISO 17560:2002—Surface chemical analysis—Secondary ion mass spectrometry—Method for depth profiling of boron in silicon

This International Standard specifies a secondary ion mass spectrometric method using magnetic‐sector or quadrupole mass spectrometers for depth profiling of boron in silicon, and using stylus profilometry or optical interferometry for depth calibration. This method is applicable to single‐crystal, polycrystal or amorphous silicon specimens with boron atomic concentrations between 1 × 10¹⁶ and 1 × 10²⁰ atoms cm^?3, and to the crater depth of 50 nm or deeper. Optical interferometry is generally applicable to crater depths in the range 0.5–5 µm. Copyright © 2004 John Wiley & Sons, Ltd.     

Alpha-activation analysis of nitrogen in boron-doped silicon single crystal

The rapid dissolution of silicon and the substoichiometric separation of¹⁸F were studied in order to determine nitrogen in a boron-doped silicon single crystal by activation analysis via¹⁵N(,n)¹⁸F. The silicon dissolution method was developed by using a nitric acid-based solution containing a known amount of ammonium fluoride, instead of hydrofluoric acid, as the¹⁸F carrier. The silicon could be dissolved to a depth of 100 m with a 10 mm Ø in 9 minutes. The conditions for¹⁸F steam distillation and substoichiometric precipitation as lanthanum fluoride were improved. 50% of the fluorine could be separated substoichiometrically even though the carrier amount was increased from 6–12 mmol to more than 16 mmol in order to add it to the dissolving solution. This dissolution method and improved substoichiometric separation were used to determine nitrogen in a boron-doped silicon single crystal. The nitrogen concentration was found to be less than the detection limit (50 ppb).     

Evaluation of minor element concentrations in potatoes using laser-induced breakdown spectroscopy

We have performed spectroscopic analysis of the plasma generated by Nd:YAG laser irradiation of flesh and skin of fresh potatoes. From the spectra recorded with an Echelle spectrometer 11 minor elements have been identified. Their relative concentrations were estimated by comparing the measured spectra to the spectral radiance computed for a plasma in local thermal equilibrium. According the moderate plasma temperature of about 6500 K at the time of spectroscopic observation, the electrons are essentially generated by the ionization of the minor metal atoms, making plasma modeling possible although the organic elements may be out of equilibrium. Among the spectral lines selected for the analysis, the Na I 588.99 and 589.59 nm doublet was found to be partially self-absorbed allowing us to estimate the number density of sodium atoms. The value was found to agree with the number density predicted by the plasma model. As a result, the relative concentrations of the detected minor elements have been estimated for both the flesh and skin of the potatoes. Among these, aluminum and silicon were found to have relatively large mass fractions in the potato skin whereas their presence was not detected in the flesh. The present study shows that laser-induced breakdown spectroscopy is a promising tool to measure the elemental composition of fresh vegetables without any sample preparation.     

Molecular structure of organic micro-crystals characterised by atomic force microscopy

In this study we show that the spin-coating technique can be used to prepare micrometer-sized crystals of organic molecules. Hydrophilic silicon wafers were spin-coated with chloroform solutions of rodlike bicyclohexylidene oximes 1–3. Atomic force microscopy images show that well-defined micro-crystals of 1 and 3 deposit on the silicon surface, which can be imaged with molecular resolution. The crystallographic dimensions derived from the atomic force microscope images correspond well with single crystal X-ray diffraction data.     

Die Anwendung radiochemischer Untersuchungsmethoden auf die Probleme der Halbleiter- und Reinststoffanalyse

With ultrapure materials it is necessary to investigate, among other parameters, the impurities and the local distribution of impurities and doping elements. Activation analysis techniques have proved highly suitable for this purpose, their advantages being extreme sensitivity of detection, a broad measure of freedom from blank values, the application of an absolute method of analysis and simultaneous coverage of a broad spectrum of elements. The capacity of autoradiography for giving inhomogeneities a visible form can be exploited to derive valuable analytical information about 50 elements on the periodic table. By employing radiotracer techniques it is possible to obtain important information leading to the optimization of manufacturing and fabrication procedures. The above advantages and the wide ranging applications of these methods are demonstrated here by way of results from radiochemical investigations of about 30 problems arising from semiconductor technology. Autoradiographs illustrate that doping and impurity elements deposit in swirls, striations and defects in the crystal lattice, e.g. in silicon, quartz, LiNbO₃, and may result in undesirable crystalline properties. Results from activation analyses demonstrate, among other phenomena, the intrinsic gettering effect with oxygen segregations in silicion, the introduction of impurities in ion-implanted materials through sputtering in a vacuum tube, increased take up of impurities under high-pressure oxidation of silicon and the purifying effect of sapphire liquefaction and of controlled silicon solidification. The capabilities of radiotracer techniques are demonstrated by investigations of zone refining and silicon wafer cleaning.     

Recent results of synchrotron radiation induced total reflection X-ray fluorescence analysis at HASYLAB,beamline L

At the Hamburger Synchrotronstrahlungslabor (HASYLAB), Beamline L, a vacuum chamber for synchrotron radiation-induced total reflection X-ray fluorescence analysis, is now available which can easily be installed using the adjustment components for microanalysis present at this beamline. The detector is now in the final version of a Vortex silicon drift detector with 50-mm² active area from Radiant Detector Technologies. With the Ni/C multilayer monochromator set to 17 keV extrapolated detection limits of 8 fg were obtained using the 50-mm² silicon drift detector with 1000 s live time on a sample containing 100 pg of Ni.Various applications are presented, especially of samples which are available in very small amounts: As synchrotron radiation-induced total reflection X-ray fluorescence analysis is much more sensitive than tube-excited total reflection X-ray fluorescence analysis, the sampling time of aerosol samples can be diminished, resulting in a more precise time resolution of atmospheric events. Aerosols, directly sampled on Si reflectors in an impactor were investigated. A further application was the determination of contamination elements in a slurry of high-purity Al₂O₃. No digestion is required; the sample is pipetted and dried before analysis. A comparison with laboratory total reflection X-ray fluorescence analysis showed the higher sensitivity of synchrotron radiation-induced total reflection X-ray fluorescence analysis, more contamination elements could be detected. Using the Si-111 crystal monochromator also available at beamline L, XANES measurements to determine the chemical state were performed. This is only possible with lower sensitivity as the flux transmitted by the crystal monochromator is about a factor of 100 lower than that transmitted by the multilayer monochromator. Preliminary results of X-ray absorption near-edge structure measurements for As in xylem sap from cucumber plants fed with As(III) and As(V) are reported. Detection limits of 170 ng/l of As in xylem sap were achieved.     

多孔硅的制备与光伏特性研究

采用特制的电解池在不同条件下制备了一系列多孔硅样品。通过测定其ＳＰＳ发现，多孔硅的ＳＰＳ特征带同单晶硅相比有明显蓝移，并且随制备条件不同，蓝移效应也不同。电解质中ＨＦ浓度和电解时间对基ＳＰＳ响应有明显影响，这一现象的出现主要归因于最子线阵的生成。     

Binary optical encoding strategy for multiplex assay

A binary optical encoding strategy is proposed to meet the increasing requirements of multiplex bioassays. As illustrated in fluorescence immunodetection of multiplex antigen molecules, photonic crystal beads (PCBs) and quantum dots (QDs) can be used as biomolecular microcarriers and fluorescence labels, respectively. The categories of antigens were deciphered by the binary combination of optical spectra of PCBs and QDs as independent encoding elements. The number of categories that could be detected was theoretically m × n, where m and n represent the number of encoding PCBs and QDs, respectively. In addition, the concentrations of the antigens were determined by the fluorescence signals of the QDs. Results of sensitivity analysis indicate that a low-level detection of 58 pg/mL was achieved. Because of the special nanostructures of these two encoding elements, the binary encoding strategy demonstrated its superiority and practicability when compared with single PCB or QD encoding. This supports potential application in multiplex bioassays.