Improvement of p+ contact resistance through optimal boron distribution TiSi2/P+ interface for 0.18 μm DRAM technology and beyond

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 BF ₂ 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