Cobalt disilicide formed by rapid thermal annealing and throughmetal arsenic implantation
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Cobalt disilicide CoSi2 of a specific resistivity of 23 /uficm was formed by the solid phase reaction of cobalt and silicon in the phase sequence of Co2Si, CoSi, and CoSi2 by use of rapid thermal annealing. The through-metal arsenic implantation caused the mixing of cobalt with the silicon substrate and the formation of cobalt silicides. A significant lateral growth of cobalt silicides was observed in samples subjected to one-step rapid thermal annealing process at 900 °C without through-metal ion implantation. Ion beam mixing reduced this lateral silicide growth efficiently, but resulted in a higher density of cobalt atoms remaining in the silicon oxide film than after rapid thermal annealing, as revealed by vapor phase decomposition atomic absorption spectroscopy.
I. INTRODUCTION When devices of MOS VLSI circuits were scaled down into the submicrometer range in recent years for higher performance and density, the RC delay due to the resistance of interconnections turned out to be one dominant factor in determining the circuit speed. Also, the widely used aluminum-silicon contact structure is not appropriate to shallow pn junctions because Al shows the so-called "spike effect". Therefore new materials must be used to reduce the interconnection resistance, the series resistances of contacts and source-drain regions, and to prevent the spike effect. Mainly because of their low resistivity and their superior chemical and thermal properties,1 the transition metal silicides have found applications as ohmic contact material and gate and interconnection metallization.2'3 On the other hand, the applications of group VIII metal silicides in VLSI are very few, since they were considered to have poor high-temperature (T ^ 900 °C) stability.1 Recently, the demand for shallower junction depths and smaller device dimensions has resulted in the lowering of the highest process temperature, and thus group VIII metal silicides, especially CoSi2, may be applied to the devices. CoSi2 could be an attractive alternative to TiSi2, since their high-temperature stabilities and electrical resistivities are similar. Furthermore, it is supposed that it should be easier with cobalt to avoid the silicide bridge effect since Co does not react with SiO 2 , and unlike the formation of TiSi2, in which silicon is the dominant diffusing species, the formation of CoSi2 is dominated by metal diffusion.4 For the application of metal silicides in MOS VLSI, the polycide (poly-Si/silicide composite gate)5 and the salicide (self-aligned silicide) 6 structures are usually used. The most favorite is the salicide structure, because it involves a silicidation of both the source-drain and gate 1892 http://journals.cambridge.org
J. Mater. Res., Vol. 6, No. 9, Sep 1991
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regions, not only reducing the interconnection resistance and the series resistances of contacts and source-drain regions, but also retaining the existing processing sequence with a minimum change and maintaining the existing polysilicon-SiO2 metal-oxide-semiconductor (M
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