TRACE DETERMINATION OF URANIUM, THORIUM, CALCIUM, AND OTHER HEAVY-METALS IN HIGH-PURITY REFRACTORY-METAL SILICIDES, NIOBIUM, AND SILICON DIOXIDE WITH ISOTOPE-DILUTION MASS-SPECTROMETRY

A method for the determination of trace impurities (U, Th, Ca, Fe, Cr, Ni, Cu, and Cd) in silicides of refractory metals, in niobium, and in silicon dioxide with isotope dilution mass spectrometry (IDMS) has been developed. This method enables uranuim and thoruim analyses down to the lowest picogram per gram level with high precision and accuracy, which is especially important for the characterization of microelectronic devices. The other elements can be determined down to the low nanogram per gram level or-depending on the blank values-in some cases less. Selective chromatographic, extractive, and electrolytic procedures for the trace-matrix-separation were combined with positive thermal ionization mass spectrometry. Different samples of high-purity materials (metal and silicide powders, compact silicide, and silicon dioxide powder) for advanced technologies were analyzed.