Titanium disilicide formation on heavily doped silicon substrates

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Abstract
Titanium disilicide formation on heavily doped silicon substrates was investigated with sheet resistance measurements, elemental depth profiling, and transmission electron microscopy. As found in a previous study [H.K. Park, J. Sachitano, M. McPherson, T. Yamaguchi, and G. Lehman, J. Vac. Sci. Technol. A 2, 264 (1984)], the TiSi2 growth rate depended on the dopant concentration. The growth rate was highest on undoped substrates, intermediate on heavily phosphorus-doped substrates, and lowest on heavily arsenic-doped substrates. However, the critical dopant concentration effect reported by Park et al. was not observed. The uniformity of the titanium-silicon reaction was not seriously affected by heavy substrate doping. For heavily arsenic-doped substrates (3.0×1021 As/cm3), TiAs precipitates formed at C49 TiSi2 grain boundaries, and the C49-to-C54 transformation temperature increased to 850 °C. For heavily phosphorus-doped substrates (1.0×1021 P/cm3), no phosphides were unambiguously detected, and the C49-to-C54 transformation temperature remained below 800 °C. Discrete blocking layers at the silicide-silicon interface, such as the native silicon oxide or a dopant-rich phase, did not cause the reduction in silicide growth. Thus, it is concluded that dopant and knock-on oxygen atoms in solid solution in both the silicide and the silicon retard TiSi2 growth.