Analysis of semiconducting materials by high-resolution radiofrequency glow discharge mass spectrometry

The analytical capabilities of a high-resolution mass spectrometer in combination with a 13.56 MHz glow discharge ion source for the analysis of semiconducting materials (silicon carbide and gallium arsenide) were studied. It was shown that single positively charged ions of sample material have about 10 eV higher average energy than the ions of the discharge and residual gas. Therefore effective energy separation of the ions of analyte from the ions of the discharge and residual gas was achieved by adjusting the ion transfer optics (breadth and position of energy slit), which improves the analytical capabilities of the developed method.Some analytical applications are presented to illustrate the performance of r.f. GDMS for the bulk analysis of semiconducting materials. The results of the trace element analysis of gallium arsenide and silicon carbide samples are compared with data of independent methods (LIMS, ICP-AES, SIMS).Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthdayOn leave from the Institute of Inorganic Chemistry, 630090 Novosibirsk, Russia     

On the formation of the crystalline phases and nanostructure of silicon carbonitride layers grown on gallium arsenide substrates

The crystallization of thin silicon carbonitride layers obtained by chemical vapor deposition from silicon organic precursors on gallium arsenide substrates at 973 K in the presence of liquid gallium drops is studied. The layers grown by the vapor-liquid-solid method are studied by IR, Raman, and energy dispersive spectroscopy, scanning electron microscopy, and X-ray diffraction using synchrotron radiation in order to determine their chemical and phase composition, crystal structure, and surface morphology. Their morphology is supposed to be associated with the formation of nuclei in a gallium drop located at the surface of the gallium arsenide substrate.     

Analysis of silicon carbonitride films by laser mass spectrometry

The possibilities of laser mass spectrometry in determining the main composition of silicon carbonitride films (SiC _x N _y ) deposited on a substrate made of germanium and gallium arsenide are considered. The conditions of laser sampling were selected and the instrument was adjusted to identify the major components of films synthesized by the plasma deposition. The instrument was calibrated by neat silicon compounds to obtain quantitative data on the concentrations of carbon, nitrogen, oxygen, and silicon. A calibration method was proposed, and the concentration of hydrogen in the layers of silicon carbonitride was estimated.     

Analysis of layered AlxGa1 − xAs on gallium arsenide by electron microprobe and secondary-ion mass spectrometry

Two samples containing Al_xGa_{1 ? x}As layers (several micrometers thick) of different composition deposited on a gallium arsenide substrate were analyzed by two techniques. Electron microprobe analysis was used on a cross-section of the samples to measure layer thickness, to obtain qualitative information by means ov x-ray line scans, and to determine the composition of the layers accurately by energy-dispersive x-ray spectrometry. Depty profiles obtained by secondary-ion mass spectrometry were used to study depth resolution at large depth ranges. Results obtained by the two techniques are in excellent agreement and compare favourably with other published results concerning the same type of sample.     

Spectrophotometric extractive titrations-II Determination in gallium arsenide of the sum of metals extractable with dithizone

A procedure for the determination of the sum of metals, which are extractable with dithizone, in gallium arsenide is given. After the dissolution of the sample the impurities are extracted with several portions of 10(-4)M dithizone in carbon tetrachloride, gallium being screened by tartrate ion. The excess of the reagent is extracted into 0.1M aqueous ammonia and after stripping into carbon tetrachloride the dithizone is determined by spectrophotometric extractive titration. The effect of pH is considered. The limit of detection, based on the evaluation of twenty blanks, is 2.30 x 10(-8) mole, the equivalent of 1.50 mug of zinc.     

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.     

Substoichiometric determination of trace impurities in high-purity materials by radioactivation analysis

The substoichiometric determination of some impurities in gallium arsenide and selenium supplied by OEC and IUPAC, respectively, as reference materials for radioactivation analysis is described.     

How gallium arsenide wafers are made

Ten Japanese gallium arsenide wafer manufacturers voluntarily formed The Japan Manufacturers' Society of Compound Semiconductor Materials (JAMS-CS) in 1983. This report summarizes the theories, the systems, and the operations of gallium arsenide production: the gradient freeze (GF) method, the liquidencapsulated Czochralski (LEC) method, the wafer processing, the vapor-phase epitaxial (VPE) growth method, the liquid-phase epitaxial (LPE) growth method, the metalorganic chemical vapor deposition (MO-CVD) method and the molecular beam epitaxial (MBE) method.     

Experimental shift allowance in the deconvolution of SIMS depth profiles

We study the deconvolution of the secondary ion mass spectrometry (SIMS) depth profiles of silicon and gallium arsenide structures with doped thin layers. Special attention is paid to allowance for the instrumental shift of experimental SIMS depth profiles. This effect is taken into account by using Hofmann's mixing‐roughness‐information depth model to determine the depth resolution function. The ill‐posed inverse problem is solved in the Fourier space using the Tikhonov regularization method. The proposed deconvolution algorithm has been tested on various simulated and real structures. It is shown that the algorithm can improve the SIMS depth profiling relevancy and depth resolution. The implemented shift allowance method avoids significant systematic errors of determination of the near‐surface delta‐doped layer position. Copyright © 2013 John Wiley & Sons, Ltd.     

The preparation and properties of chromium oxide nanolayers on semiconducting matrices

Ultrathin chromium oxide layers (nanostructures) were synthesized on the (100) and (110) silicon and gallium arsenide surfaces by molecular layering (atom layer deposition). Technological factors were shown to influence the main rules governing nanolayer formation, nanolayer composition, and some electric nanolayer characteristics.     

Determination of nickel,gold and silver in gallium arsenide by radioactivation analysis based on the quantitative isotope dilution principle

A method of radioactivation analysis has been developed for the determination of Ni, Au and Ag impurities in gallium arsenide. The separation and substoichiometric extraction of these elements were studied and analytical procedures are suggested for their determination. All components are separated by suitable procedures and determined by substoichiometric methods. Ni is extracted as diethyldithiocarbamate into toluene, Au as a complex of rhodamine-B in chloroform, and Ag as dithizonate in carbon tetrachloride. The contents of Ni, Au and Ag in a gallium arsenide crystal with a carrier concentration of 1.8·10¹⁶/cm³ were 0.05–0.08, 0.006–0.008 and 0.002–0.005 ppm, respectively.     

Determination of boron in silicon-doped gallium arsenide by electrothermal atomic absorption spectrometry and ultraviolet-visible spectrophotometry

Two methods have been developed for the determination of boron impurities in silicon-doped gallium arsenide (GaAs) for electronics. The first method employs the electrothermal atomic absorption spectrometry (ETAAS), the second, the UV-Vis molecular absorption spectrophotomety. In both cases the GaAs sample is decomposed with aqua regia (1+1). To prevent Ga(III) interference on the ETAAS determination of boron, a double extraction of the chlorogallic acid (HGaCl4) in diethyl ether is performed. To improve the overall ETAAS performance, the graphite tubes were pre-treated with iridium(III) and tungsten(IV). A mixed chemical modifier containing Ni(II), Sr(II) and citric acid was also used. The characteristic mass (m0) is 301 +/- 47 pg and the detection limit (3sB) is 2.4 microg g(-1). The classic UV-Vis spectrophotometric procedure using curcumin was also extended to the determination of boron in GaAs. By masking Ga(III) with EDTA and a preliminary extraction of boron with 2-ethyl-hexane 1,3-diol, performed on a semi-micro scale, a detection limit of 0.6 microg g(-1) was achieved. Both methods were applied to the analysis of two Si-doped GaAs samples which were suspected of being boron-contaminated. Results are compared with those obtained by direct analysis of the decomposed sample solution using the inductively coupled plasma atomic emission spectrometry (ICP-AES).     

Investigation of silicon dioxide films by neutron activation analysis and autoradiography

Investigations of insulating silicon dioxide films formed on silicon epitaxial layers are reported. Activation analysis and surface autoradiography were used to determine the concentration distribution and precipitation of contaminants in the internal part of the films and on the surfaces. The aim of this work was to study the origin of the contaminants by sampling each technological product following thermal oxidation, doped oxide deposition, heating and metallizing. Under the given conditions the following detection limits of impurities could be obtained in silicon dioxide films: Na=80 ppb, Sb=100 ppb, Cu=20 ppb and Au=5 ppb.     

Determination of relative sensitivity factors for trace element analysis of solar cell silicon by fast-flow glow discharge mass spectrometry

A commercially available Element GD, the latest generation of glow discharge mass spectrometry (GDMS), has been used for quantitative analysis of impurities in silicon for photovoltaic applications (PV silicon). In order to be able to accurately measure impurities in silicon, relative sensitivity factors (RSFs) need to be determined. These factors are, currently, given only for steel matrices. In this study, standard silicon materials with known levels of impurities have been produced and independent analytical methods have been used for determining the RSFs for silicon matrices. It has been found that the tuning parameters of the Element GD, mainly the discharge gas flow rate, influence the RSF values. In addition, it has been found that RSF values are matrix specific; RSFs for a silicon matrix differ significantly from those for metallic conductor matrices even under identical instrumental parameters. A study of the relative reproducibility in the quantitative analysis of impurities in solar cells silicon has shown variations between 5% and 12%.     

Radiofrequency spark source mass spectrometric analysis of oxygen in undoped silicon crystals and of carbon in undoped and carbon doped gallium arsenide crystals

Radiofrequency spark source mass spectrometry is a reliable and precise analytical method to measure the amount of oxygen in silicon grown by the Czochralski technique from SiO₂ crucibles in the common range from 2ppm(atomic) to 20ppm(atomic) and in silicon grown by the floating zone technique below 0.1ppm(atomic). The technique is also excellent for the measurement of the amount of carbon in semi-insulating gallium arsenide grown under low and high pressure N₂ ambient gas by the B₂O₃ encapsulated Czochralski technique from pyrolytic BN crucibles in the common range from 0.02ppm(atomic) to 0.4ppm(atomic). The results are in rather good agreement with concentrations measured by charged particle activation analysis and consistent with those obtained using other methods.     

Substoichiometric precipitation of silicon as barium fluorosilicate

Distillation and substoichimetric precipitation for silicon have been developed for the determination of trace amounts of silicon. It is based on substoichiometric precipitation as barium fluorosilicate and the distillation of silicon tetrafluoride. The separation has been applied for the determination of silicon in gallium arsenide and NBS steel as standard reference material.     

Determination of trace impurities at the p.p.b. level in fused silica by spark-source mass spectrometry

A sample dissolution-concentration technique for the determination of trace elements in fused silica by spark-source mass spectrometry (s.s.m.s.) is described. The fused silica is dissolved by ultra-pure hydrofluoric acid, and most of the silicon tetrafluoride formed is then removed at 80–100° C, leaving behind the impurities in the solution as fluorides. After addition of ultrahigh-purity graphite and internal standards (Tl and Rb), the mixture is dried to give a sample suitable for pressing into electrodes. The method not only concentrates the trace impurities but also reduces the interferences originating from silicon oxide and carbide species in the mass spectra and thus allows the determination of a larger number of elements at p.p.b. levels. More than 30 trace impurities in 6 fused silica boules and J.T. Baker's Ultrex silicon dioxide are determined and compared with data obtained by other methods.     

Radio-frequency glow discharge ion source for high resolution mass spectrometry

A radio-frequency powered glow discharge ion source has been developed for a double-focusing mass spectrometer. The sputtering and ionization of conducting, semiconducting and insulating materials have been realized using a 13.56 MHz generator to supply the discharge operating potential. The glow discharge ion source operates stably at argon pressures of 0.1–1 hPa and radio frequency powers of 10–50 W. The influence of discharge parameters and gas inlet system on sputtering rates and ion signal intensities for semi-insulating gallium arsenide wafers has been investigated.     

Control of the composition of lanthanum gallium silicate by laser ablation inductively coupled plasma mass spectrometry

The possibilities of determining the impurities and basic components of lanthanum gallium silicate using laser ablation in combination with inductively coupled plasma mass spectrometry (LA-ICP-MS) were shown. A procedure for the determination of 54 impurity elements with the limits of determination from n × 10^?5 wt % for Mg, Ti, V, Cr, Mn, Ni, Cu, and Zn to 2 × 10^?7 wt % for U and also a procedure for the determination of a ratio between basic components were developed. It was found that the concentration ratios between gallium and lanthanum and silicon and lanthanum in the crystals of lanthanum gallium silicate remained constant upon consecutive melting operations with the addition of a charge mixture to the crucible.     

Analytical study by SEM/EDX and metallographic techniques of materials used in the iron production process during the iberian period

This work is the archaeometric study of different types of materials used in iron production in the Iberian Period (6th-2nd century b.c.). The materials were recovered in several archaeological digs (which makes it possible to date the archaeological remains) on different sites in the Levante area of the Iberian Peninsula. The samples selected for this study belong to different materials used in the ancient iron production process such as ores, slags, finished objects, etc. The use of scanning electron microscopy (SEM) is proposed to observe surface images of the samples to determine their morphological, microstructural and topographic characteristics to obtain valuable information on the materials studied. The study also proposes chemical analysis of the elements in the sample by X-ray microanalysis (SEM/EDX) which provides both qualitative and quantitative information. The archaeometric study suggests that the iron obtained was very good quality, but the process was not economically efficient when viewed from today's perspective. Furthermore, the slag produced in the furnace can be related with the slag or impurities contained in the iron. It has also been possible to relate the ores and slag, some furnace conditions, the use of fluxes and also to differentiate types of slag.