Abstract

Boron concentration was investigated at the TiSi2/p+ interface which was one of the important factors to influence on the p+ contact resistance, for 0.18 μm DRAM (Dynamic Random Access Memory) technology and beyond. During the formation of titanium silicide (TiSi2) on the p+ area, heavily doped boron junction is consumed as the silicide moves into silicon. In this paper, we obtained excellent improvement of p+ contact resistance employing the method of maximizing boron distribution at TiSi2/p+ interface, using BF2 as an implanting species. In addition, we noticed that the factors contributed to the p+ contact resistance greatly were as-deposited Ti thickness on the p+ layer, Ti/TiN annealing temperature and BF2 ion implant energy. Furthermore, we observed that fluorine influenced the interface boron concentration significantly by piling up in the defect region of the BF2 implanted layer. Thus, we propose that, in the case of less than 1200 Å-p junction, the Ti thickness should be controlled less than 50 Å on the bottom of p+ contact hole and the Ti/TiN annealing temperature should be optimized at around 750°C in order to maximize the boron concentration at the TiSi2/p+ interface.