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.     

Use of the ion microanalyzer for the characterization of bulk and epitaxial silicon and gallium arsenide

The ion microanalyzer permits a localized mass spectrometric analysis, i.e. the qualitative and quantitative analysis of the impurities contained in a small selected volume. This procedure makes possible the analysis of very thin epitaxial layers (for example silicon and gallium arsenide). As regards qualitative analysis, the apparatus is designed for the selection of ions. After the recording and analysis of the ion spectrum, a large number of the impurities present in the sample are determined qualitatively. Quantitative analysis can be performed with the equipment, but this requires the analysis of a homogeneous standard sample previously dosed by spark-source mass spectrometry. The quantitative analysis of bulk and epitaxial silicon and gallium arsenide is described and the limits of detection of the principal impurities are given. It is also shown how the possibility of localized analysis was exploited. A correlation was established between the existing impurities and the chemically revealed crystal imperfections. A comparative analysis of the distribution of the impurities in the epitaxial layers was also carried out. The periodic analysis of epitaxial layers makes it possible to follow the deterioration by contamination, if any, under the epitaxial conditions, and to improve the sample quality.     

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.     

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.     

Instrumental neutron activation analysis of high-purity gallium,arsenic, and gallium arsenide

Instrumental neutron activation analysis (INAA) has been applied to obtain useful data on impurity concentrations in ultra-pure materials whose matrix elements are strongly activated and create severe interference for several weeks after irradiation. An analytical procedure has been developed and used to determine Sc, Fe, Co, Zn, Se, Zr, Ag, In, Sn, Sb, Te, and Hg in high-purity gallium, arsenic, and gallium arsenide. Detection limits ranged from 50 ng/g for iron to 0.001 ng/g for scandium. Problems of contamination control, blank level, and standardization are discussed.     

New Electrodes with Membranes Based on Semiconductor Compounds of the AIIIBV Type

The characteristics of new electrodes with semiconducting membranes based on gallium arsenide and gallium antimonide were studied in solutions of metal salts, halides, and complexing agents. The proposed electrodes can be used as indicator electrodes in acid–base, precipitation, and complexometric potentiometric titration.     

Optimization of an rf-powered magnetron glow discharge for the trace analysis of glasses and ceramics

A radiofrequency (rf) powered planar magnetron glow discharge ion source has been designed and coupled to a double-focusing mass spectrometer. Superposition of the electrical field of the plasma in the cathode dark space and the magnetic field obtained from a ring-shaped magnet located directly behind the sample (cathode) form the electron traps and enhance the sputtering and ionization efficiency of the ion source. In order to establish optimum conditions for the trace analysis of nonconducting materials, mass spectrometric studies have been carried out on the ion signal intensities and energy distributions of analyte and discharge gas ions depending on pressure.     

Optimization of an rf-powered magnetron glow discharge for the trace analysis of glasses and ceramics

A radiofrequency (rf) powered planar magnetron glow discharge ion source has been designed and coupled to a double-focusing mass spectrometer. Superposition of the electrical field of the plasma in the cathode dark space and the magnetic field obtained from a ring-shaped magnet located directly behind the sample (cathode) form the electron traps and enhance the sputtering and ionization efficiency of the ion source. In order to establish optimum conditions for the trace analysis of nonconducting materials, mass spectrometric studies have been carried out on the ion signal intensities and energy distributions of analyte and discharge gas ions depending on pressure.     

Contribution to the characterization of reference materials for thin-film analysis in solar-energy and semiconductor technologies

A combined approach of independent surface and bulk analytical methods was applied to characterize materials that had been prepared by ion implantation of P. Co and Ni ions into high purity silicon, for use as reference materials in thin-film analysis techniques. In this characterization, high precision and accuracy of 1–2% were obtained by utilizing instrumental neutron activation analysis for the determination of the total implanted ion dose. The impact of the analytical results on the preparation procedure is discussed.     

Crystallization in low-energy deposition of titanium ions

To investigate crystallization in the ion beam deposition process, titanium ions were deposited on silicon wafers at 105 and 55 eV. As titanium is an active metal, titanium compounds are formed by absorbing backfilled or residual gas. At energy levels of 105 or 55 eV, titanium crystallizes in a NaCl-type titanium compound with the backfilling of air. In all samples, (110)-oriented crystals grew with a rectangular lattice arrangement of titanium atoms. The open channel <110> of preferentially oriented crystal growth was parallel to the direction of incident ions normal to the substrate surface.     

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.     

Use of spectroscopic techniques for the chemical analysis of biomorphic silicon carbide ceramics

Biomorphic silicon carbide ceramics are a new class of materials prepared by several complex processing steps including pre-processing (shaping, drying, high-temperature pyrolysis in an inert atmosphere) and reaction with liquid silicon to obtain silicon-carbide. The results of industrial process of synthesis (measured by the SiC content) must be evaluated by means of fast analytical methods. In the present work, diverse samples of biomorphic ceramics derived from wood are studied for to evaluate the capability of the different analytical techniques (XPS, LIBS, FT-IR and also atomic spectroscopy applied to previously dissolved samples) for the analysis of these materials. XPS and LIBS gives information about the major components, whereas XPS and FT-IR can be used to evaluate the content of SiC. On the other hand, .the use of atomic techniques (as ICP-MS and ETA-AAS) is more adequate for the analysis of metal ions, specially at trace level. The properties of ceramics depend decisively of the content of chemical elements. Major components found were C, Si, Al, S, B and Na in all cases. Previous dissolution of the samples was optimised by acid attack in an oven under microwave irradiation.     

The role of ions and UV radiation in gallium arsenide etching process

The mechanism of gallium arsenide etching in a chlorine-argon plasma was studied. The absorption-desorption model was proposed which explains an increase in etching rate upon chlorine dilution with argon by enhancement of the efficiency of active site cleaning with plasma UV radiation and ion fluxes. The processes of desorption of etching products from the surface by ions and UV photons were shown to be energetically favored. The amount of active sites cleaned per ion or photon was calculated. The addition of argon was assumed to change the proportion of active sites. Procedures for calculating fluxes of reactive species onto the surface and the probability of ultraviolet light and ion-induced desorption were detailed.     

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.     

Chemical Analysis of Inorganic and Organic Surfaces and Thin Films by Static Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS)

By using mass spectrometry to analyze the atomic and molecular secondary ions that are emitted from a solid surface when bombarded with ions, one obtains detailed information about the chemical composition of the surface. A time-of-flight mass spectrometer is especially suitable for the analysis of secondary ions because of its high transmission, high mass resolution, and ability to detect ions of different masses simultaneously. By using a finely focused primary ion beam it is also possible to analyze microareas and generate surface images with a lateral resolution of 0.1 μm or less. Static time-of-flight secondary ion mass spectrometry (TOF-SIMS) allows monolayer imaging and local analysis of monolayers with high sensitivity, a wide mass range, high mass resolution, and high lateral resolution. Besides information on elements and isotopes, the technique yields direct information on the molecular level and can also be used to analyze surface species of high molecular mass that are thermally unstable and cannot be vaporized. The method can be applied to practically all types of materials and sample forms, including insulators in particular. In this article the basic principles of TOF-SIMS are explained, and its analytical capabilities for both large area and imaging applications are illustrated by examples. These include silicon surfaces (both uniform and structured), thermally unstable organic molecules on surfaces, synthetic polymers, and synthetically prepared molecular surface films, particles, and fibers. Emitted neutral particles can also be analyzed by postionization with a laser, and the possibilities of this technique are discussed.     

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.     

Applications of Inorganic Polymeric Materials II: Polysilanes

Polysilanes which cover one of the most attractive and challenging fields, are high molecular weight polymers with inorganic elements in their backbone. These materials have silicon atoms in their main chain and exhibit unique properties resulting from the easy delocalization of sigma electrons in the Si─Si bonds. There are many technical uses as well as applications of these materials such as precursors of silicon carbide ceramics; a strengthening agent in porous ceramic; imaging materials in microlithography; photoiniting in radical reactions; and photoconducting, conducting, and semiconducting which are due to the unusual mobility of sigma electrons. In this work, the main structural features, properties, and some other important and recent applications of polysilanes are discussed.     

‘Fast atom bombardment’—A rediscovered method for mass spectrometry

In 1966, Devienne and co-workers studied extensively the sputtering of various target materials by a high energy molecular beam obtained by charge exchange. They obtained secondary ions that characterized for instance, organic and biological materials. These ions were analysed by mass spectrometry. This method was developed to be patented and many devices were studied. The principle of the apparatus constructed is very simple. An ion source produces an ion current of some microamperes. The ions are accelerated at some keV, and injected into a collision chamber in order to obtain a neutral beam by resonant charge exchange. The residual ions are deflected and this beam bombards the target. The target itself is surrounded by a small metal cylinder which is held at an appropriate potential to extract the positive or negative secondary ions formed. The ion beam is accelerated and focused into the entrance slit of a mass spectrometer. After the first devices, two types of apparatus were built in 1973 and 1975. With the first one, the analysis of the masses was obtained only by an electromagnet. The energy range of the secondary ions varied from 1 to 10 keV. The second apparatus was formed by an electromagnet, a dissociation chamber, and an electrostatic analyser. With this apparatus, it was possible to measure directly masses as large as 6000 daltons. With the first apparatus it was possible to study the adsorption of oxygen on silicon, and to obtain spectra, of many organics such as camphor, nitrodiphenylamine and, as in the earlier device, the spectrum of a non-volatile organic liquid diethylhexyl azelate, was obtained. After studies on different uranium compounds and their dissociations, the second apparatus was devoted to the formation and study of the chemical properties of clusters.     

Gravimetric determination of free carbon and silicon carbide in silica fume

Silica fume is formed as a by-product in the manufacture of silicon from quartzite. This paper describes an analytical method for the determination of free carbon and silicon carbide in silica fume. The silicon carbide was determined after removal of free carbon, amorphous silica, crystalline silica, graphite and silicon from the fume. The free carbon content was found to vary from 2 to 8% while the silicon carbide content ranged from 1 to 5%. X-ray diffraction, thermal analysis, scanning electron microscopy and Fourier Transform infrared spectroscopy were used to validate the steps used in the analytical procedure. The purpose of determining the free carbon and silicon carbide content of the fume is to help understand the efficiency of the reduction process and mechanism of the reaction.     

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.