The sheet resistance of TiSi2 films formed on patterned sub-half micron n+ polysilicon lines has been observed to be higher than the sheet resistance of unpatterned blanket TiSi2 films. We have investigated this phenomenon, and determined that the TiSi2 thickness is not a function of linewidth, and that the resistivity increase in narrow n+ lines is caused primarily by incomplete phase transformation to the low-resistivity C54 phase. We have determined a physical model for the kinetics of this phase transformation, based on an Arrhenius-type atomic re-arrangement process, and we have determined an activation energy (Ea) of phase transformation for different linewidths. We have observed that this Ea increases non-linearly as a function of decreasing linewidth, contrary to conventional belief. We have hypothesized that this increase is due to increasing dominance of edge-related phenomena such as contaminant segregation, strain etc. Finally, we have demonstrated that by supplying this Ea through a high temperature (825°C) anneal, even applied for a short time (15 s), low sheet resistances (<4 Ω/ü) can be obtained down to 0.35 μ m lines.
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Karen Maex. “Suicides for integrated circuits: TiSi2 and CoSi2”. Materials Science and Engineering, R11: 53, 1993.
R.W. Mann and L. A. Clevenger. “The C49 to C54 Phase Transformation in TiSi2 thin Films”. J. Electrochem. Soc, 141(5): 1347, 1994.
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Apte, P.P., Pollack, G. A Model for Low-Resistivity TiSi2 Formation on Narrow Polysilicon Lines.. MRS Online Proceedings Library 355, 539–544 (1994). https://doi.org/10.1557/PROC-355-539