Reaction and thermal stability of cobalt disilicide on polysilicon resulting from a Si/Ti/Co multilayer system

The formation and thermal stability of ${\mathrm{CoSi}}_{\mathrm{2}}$ has been investigated using a poly-Si/Ti/Co multilayer structure. The presence of the Ti layer allows the phase formation by a single step with an optimum reaction temperature in the range between 750 and 850 °C. The layer agglomerates at temperatures higher than 950 °C. Sheet resistance measurements have been used to monitor the kinetics of the agglomeration process. The dependence of both the sheet resistance and the thermal stability on the film thickness has been studied in detail. The agglomeration process is thermally activated with an energy of ∼3.9 eV, lower than the value 5.6 eV measured in ${\mathrm{CoSi}}_2$ layers formed by direct reaction of Co with polycrystalline silicon. These activation energies have been correlated to the different layer structures. In the silicide formed without the Ti thin film, the grains are columnar, while the presence of Ti causes a random distribution in the grain shape and smaller size. The low thermal stability of the ${\mathrm{CoSi}}_2$ layer on polysilicon can be a problem to use the Ti/Co bilayer process in self-aligned complementary metal–oxide–semiconductor technology.