Behavior of Molybdenum in Silicon Evaluated for Integrated Circuit Processing

Mo is introduced into Si integrated circuits inadvertently during processing, often during Si epitaxial growth, high temperature furnace treatments, or BF 2 ion implantation. Quantitative secondary ion mass spectrometry measurement of Mo concentrations in Si introduced by BF 2 implantation is complicated by mass aliasing of 98 Mo 2+ and BF 2 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 concentrations as high as 5 X 10 14 cm -3 , but present evidence that the solubility of 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 recombination center as Fe in Si. And in addition, Mo is not gettered to either p + epitaxial substrates or by high energy B implantation. Process engineers and circuit designers can expect little effect of Mo contamination on metal oxide semiconductor devices but can assume that trace Mo contamination may cause leakage current in bipolar devices.