Trace analysis semiconductors

Semiconductors Process gases, plasma gases, substrate analysis for contaminants Gas composition analysis Raw materials screening Trace analysis Quality control... 

Neutron activation is not a widely used method (Fig. 17.8). Some of its applications include characterisation of materials (e.g. high purity metals, semiconductors), the study of the distribution of chemical elements within fossils, ultra-trace analysis in archaeology and geology, and the study of volcanoes. 

Cali, J. P. Ed.) Trace Analysis of Semiconductor Materials. Oxford Pergamon Press 1964. 

Surface chemistry, in general, is an area in which the ability to selectively modify the chemical and physical properties of an interface is highly desirable. The synthetic chemistry of surfaces is now in a developing stage, particularly with respect to the attachment of electroactive redox sites to metal or semiconductor surfaces (L-3). Single component and bilayer (4) electroactive films have been a field of intense research activity since their applications are apparent in catalysis, solar energy conversion, directed charge transfer, electrochromic devices, and trace analysis. 

The method of spark source MS was developed by Dempster in 1935 . During the last two or three decades, this technique was utilized in the trace analysis of impurities in high purity elements, such as semiconductors, superconductors, nuclear reactor components and magnetic, thermoelectric or luminescent materials. There is an urgent necessity for the determination of trace elements in these materials, because they are characterized by the presence or absence of particular elements in the ppm or ppb range. 

The possibility of determining traces of elements arose in the 1920s with the development of spectrophotometry, spectroscopic methods, and polarography. Trace analysis was carried out very intensively and with great sophistication in connection with the development and production of the first atomic bomb. Later, it received an important stimulus from the development of novel materials, especially semiconductors. 

Today, more areas than ever depend on the results of trace analysis Nuclear energy, production of semiconductors and ultrapure substances, metallurgy, materials research and production, geology. mineralogy, oceanography, medicine, an-... 

Lasers represent a special type of light source [16], [21], [60], [61]. They are used in trace analysis by fluorescence measurement or laser-induced fluorescence (LIF) (- Laser Analytical Spectroscopy) [62] - [64], in high-resolution spectroscopy, and in polarimetry for the detection of very small amounts of materials. Lasers can be of the gas. solid, or dye type [21]. In dye lasers, solutions of dyes are pumped optially by another laser or a flash lamp and then show induced emi.s-sion in some regions of their fluorescence bands. By tuning the resonator the decoupled dye laser line can be varied to a limited extent, so that what may be termed sequential laser spectrometers can be constructed [65]. In modern semiconductor lasers, pressure and temperature can also be used to detune the emission wavelength by 20-30nm [66], [67]. 

AutoNeutralization also has to be applied for trace analysis of anions in bases such as sodium hydroxide, ammonium hydroxide, tetramethylammonium hydroxide, and tetrabutylammonium hydroxide, because the high concentration of hydroxide in the matrix would in practice act as an eluent and thus render impossible the preconcentration of anions in a concentrator column [247]. In the semiconductor industry, quaternary ammonium bases serve as developers for light-sensitive paints and, therefore, also have to be investigated for anions responsible for corrosion. As shown in Figure 10.145, detection limits in the midmicrogram/Liter range are obtained without difficulty when applying AutoNeutralization. 

The determination of molecular formulas via accurate mass measurements relies on isotopic masses accurate to at least 1 in 10 [10]. Elemental trace analysis is required for the detection of radioactive nuclides in the environment, of transition metals such as Pt in exhaust fumes from automobiles [11], and in the quality control of low-sulfur fuels for the same. All electronic devices demand for high-purity semiconductors and the properties of alloys are critically influenced by trace elements [12]. Age determinations from isotope ratios are applied in archeology, paleontology, and geology [4,13,14]. More recently, elemental MS and biomedical MS are jointly employed to unveil the presence and preferably location of metals in proteins or DNA as well as their lateral distribution in tissues [15-18], a field of research basically going back to seminal work by Houk in 1980... 

Anatoliy Aleksandrovich Kaplin (October 20, 1937-July 27, 1989) (Fig. 5.4.3.4) has developed SV for the determination of traces in semiconductor and other high-purity materials [51]. He was an excellent organizer, not only of research work (he has supervised 20 PhD theses) but also of conferences, e.g., of four All-Union Conferences on Stripping Voltammetry in Tomsk (1973,1982,1986,1990) under the chairmanship of Stromberg. Parallel to Ye. Ya. Neyman who worked in Moscow, Kaplin started to study the formation of complex amalgams, intermetaUic compounds in mercury, and solid solutions under the conditions of SV. Anodic currents of such systems were described by Kaplin on the basis of regular solution thermodynamics. Kaplin defended his doctoral thesis entitled Inverse voltammetric analysis of microsamples, crystal layers and films before a conunission in Moscow. 

Multi-element trace analysis by LA-ICP-MS of high-purity metals, semiconductors and insulators (e.g. ceramics) is often limited by the lack of suitable SRMs of the same matrix composition. In addition, a significant number of trace element concentrations are not certified in the specific commercially available SRMs. 

The detection and determination of traces of cobalt is of concern in such diverse areas as soflds, plants, fertilizers (qv), stainless and other steels for nuclear energy equipment (see Steel), high purity fissile materials (U, Th), refractory metals (Ta, Nb, Mo, and W), and semiconductors (qv). Useful techniques are spectrophotometry, polarography, emission spectrography, flame photometry, x-ray fluorescence, activation analysis, tracers, and mass spectrography, chromatography, and ion exchange (19) (see Analytical TffiTHODS Spectroscopy, optical Trace and residue analysis). 

In Total Reflection X-Ray Fluorescence Analysis (TXRF), the sutface of a solid specimen is exposed to an X-ray beam in grazing geometry. The angle of incidence is kept below the critical angle for total reflection, which is determined by the electron density in the specimen surface layer, and is on the order of mrad. With total reflection, only a few nm of the surface layer are penetrated by the X rays, and the surface is excited to emit characteristic X-ray fluorescence radiation. The energy spectrum recorded by the detector contains quantitative information about the elemental composition and, especially, the trace impurity content of the surface, e.g., semiconductor wafers. TXRF requires a specular surface of the specimen with regard to the primary X-ray light. 

NAA is well suited for Si semiconductor impurities analysis. The sensitivity and the bulk mode of analysis make this an important tool for controlling trace impurities during crystal growth or fer monitoring cleanliness of various processing operations for device manufacturing. It is expected that research reactors will ser e as the central analytical facilities for NAA in the industry. Since reactors are already set up to handle radioactive materials and waste, this makes an attractive choice over installing individual facilities in industries. 

The technique can be used to measure concentrations in the range 10 6-10 9M and as such is eminently suitable for the determination of trace metal impurities of recent years it has found application in the analysis of semiconductor materials, in the investigation of pollution problems, and in speciation studies. 

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