On the resistivity of TiSi2: The implication for low-temperature applications

The electrical resistivity of TiSi
2
formed on polysilicon implanted with phosphorus and arsenic and on n
⁺
and p
⁺
diffusions implanted with arsenic and boron was measured in the 4.2-300 K temperature range. It is found that in all cases, the resistivity is reduced by a factor of 3-4 when TiSi
2
is cooled from room to liquid-nitrogen temperature. Sheet resistance as low as 1 Ω/sq. at liquid-nitrogen temperature can be easily achieved for self-aligned thin TiSi
2
layers over polysilicon and diffusion regions, which is very attractive for low-temperature CMOS applications. The residual resistivity ratio, which is a measure of the electron mean free path, decreases with growing surface concentration of dopants, regardless of doping species. The analysis of thickness effects in terms of surface scattering and of grain boundary resistivity models, suggests that degradation of sheet resistance R
s
with increased implantation dose is due only partly to the difficulty in forming thick enough TiSi
2
at high doses, and that dopant impurities segregated at the grain boundaries can account for the observed increase.