Titanium disilicide formation on heavily doped silicon substrates

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.