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Mass Spectrographic Technique for the Determination of Molybdenum Additive in Tantalum Oxide Capacitor Films

Volume 22, Number 4 (Aug. 1968) Page 318-320

Malm, D.L.

Recent analytical demands in thin-film technology require a means for quantitative measurements of intentionally added impurities in sputtered tantalum capacitor films. The inherent high sensitivity and surface-sensing ability of the rf vacuum spark source mass spectograph suggest its usefulness for this study [A. J. Ahearn, "Sixth National Symposium on Vacuum Technology Transactions" (Pergamon Press, Inc., New York, 1960)]. It has been demonstrated that with the aid of an internal standard and a sample-scanning technique that samples the film on the substrate, thus eliminating any chemical separations, quantitative estimates of molybdenum additive in films 4000 Å thick can be made with an average deviation of ±23%. A concentration range of 0.02% to 3.1% atomic fraction of molybdenum in tantalum films was studied. Because adequate sensitivity is attained without consuming the entire available sample, it is reasonable to predict that sensitivities of 10 ppm atomic or less may be reached. Results show a linear increase in the molybdenum concentration as the molybdenum-to-tantalum sputtering-surface ratio increases. Once this relationship has been established, films with the desired molybdenum concentration can be produced without the need for further chemical analysis. Mass spectrographic results also indicate that the molybdenum additive is homogeneously distributed in the tantalum film.