Multielement ultratrace analysis of molybdenum with high performance secondary ion mass spectrometry
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H.M. OrtnerandP. Wilhartitz Metallwerk Plansee GmbH., A-6600 Reutte, Austria (Received 25 November 1987; accepted 21 March 1988) Electron beam melting has been used to obtain ultrapure refractory metals that are gaining importance in metal oxide semiconductor-very large scale integration (MOS-VLSI) processing technology, fusion reactor technology, or as superconducting materials. Although the technology of electron beam melting is well established in the field of production of very clean refractory metals, little is known about the limitations of the method because the impurity level of the final products is frequently below the detection power of common methods for trace analysis. Characterization of these materials can be accomplished primarily by in situ methods like neutron activation analysis and mass spectrometric methods [glow discharge mass spectrometry (GDMS), secondary ion mass spectrometry (SIMS) ]. A suitable method for quantitative multielement ultratrace bulk analysis of molybdenum with SIMS has been developed. Detection limits of the analyzed elements from 10~ 7 g/g down to 10~ 12 g/g have been found. Additional information about the distribution of the trace elements has been accumulated.
I. INTRODUCTION New industrial applications of refractory metals, e.g., as gate materials in metal oxide semiconductorvery large scale integration (MOS-VLSI) technology,1 as first wall materials in nuclear industry, 23 as superconducting materials or alloys,4"6 and the like, prompted the development of purification processes for these materials. Three essential steps are used to achieve the required purity. The first one is multiple recrystallization of tungsten and molybdenum acids or other adequate compounds that are then reduced under hydrogen to get pure metal powders. The second step is the sintering process. The major technique for further purification of the material is multiple electron beam melting, which can be performed with different arrangements.7 In the third step purification is accomplished due to the evaporation of trace elements at the melting temperature Of the refractory metal in vacuum. Although the technology of electron beam melting is well established for the preparation of very clean refractory metals,8 little is known about the limits of this method, because the residual trace element concentrations in an ingot that has been melted one or more times are frequently below the detection limits of common methods for trace analysis like electrothermal atomic a)
Address for correspondence: Dr. M. Grasserbauer, Institute for Analytical Chemistry, University of Technology Vienna, Getreidemarkt 9, A-1060 Vienna, Austria.
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J. Mater. Res. 3 (4), Jul/Aug 1988
http://journals.cambridge.org
absorption spectrometry (ET-AAS), inductively coupled plasma-optical emission spectrometry (ICPOES), and spark source mass spectrometry (SSMS). Consequently, questions concerning sufficient product purity for use as sputter target material for thin-film production in microelectronic technology often cannot b
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