Behavior of molybdenum in silicon evaluated for integrated circuit processing

Mo is introduced into Si integrated circuits inadvertently during processin g, often during Si epitaxial growth, high temperature fur nace treatments, or BF2 ion implantation. Quantitative secondary ion mass spectrometry measu rement of Mo concentrations in Si introduced by BF2 implantation is complic ated by mass aliasing of Mo-98(2+) and BF2 and by unexpected isotope ratios . Employing deep level transient spectroscopy depth profiling of implanted Mo in Si, we determine for the first time the diffusivity of Mo in Si, D = 0.26 exp[(-2.2) eV/kT] cm(2)/s. We observe soluble Mo in Si at concentratio ns as high as 5 X 10(14) cm(-3), but present evidence that the solubility o f Mo in Si is mediated by crystal defects and proximity of the surface. Mo does reduce carrier lifetime in Si, although it is not as an effective reco mbination center as Fe in Si. And in addition, Mo is not gettered to either p(+) epitaxial substrates or by high energy B implantation. Process engine ers and circuit designers can expect little effect of Mo contamination on m etal oxide semiconductor devices but can assume that trace Mo contamination may cause leakage current in bipolar devices. (C) 1999 The Electrochemical Society. S0013-4651(98)08-093-8. All rights reserved.