TRACE ANALYSIS OF MICROELECTRONICALLY RELEVANT HEAVY-METALS IN HIGH-PURITY TITANIUM WITH ISOTOPE-DILUTION MASS-SPECTROMETRY

Because titanium is increasingly used in microelectronic devices, a method of isotope dilution mass spectroscopy (IDMS) has been developed for the reliable determination of traces of relevant heavy metals (U, Th, Cu, Pb, Cd, Cr, Ni, and Fe) in high-purity titanium primary materials. The measurements of isotope ratios were carried out with a thermal ionization quadrupole mass spectrometer using positive thermal ions formed by a single- or double-filament ion source, except for thorium where an inductively coupled plasma mass spectrometer was applied. Different separation techniques (ion exchange chromatography, extraction, electrolytic deposition, co-precipitation) were used for the trace/matrix separation and the element-specific isolation of the trace elements to be determined. The detection limits obtained were (in ng/g) as follows: U, Th = 0.07; Cu = 1; Cd = 1.7; Ni = 4; Pb = 6; and Fe = 35. Three titanium samples of different purity were analyzed with concentrations in the following range (in mug/g): U, Th, (<0.07 X 10(-3))-0.09; Cd <0.002-0.7; Cu, Ni, Pb, Cr = 0.01-30; and Fe = 7-(6 x 10(3)). The IDMS results of one titanium sputter target were compared with those of two different GDMS laboratories which showed the urgent necessity of the application of independent and reliable analytical methods.