Simultaneous formation of TiN and TiSi2 by lamp annealing in NH3 ambient and its application to diffusion barriers

Abstract

The dependence of TiN/TiSi₂ bilayer formation on Si by lamp annealing of Ti upon annealing temperature, ambients, and impurity in Si was investigated. In NH₃ ambient, nitridation ratio on undoped Si at 680 and 800 °C is 40% and 25%, respectively. When annealing is performed in N₂, the nitridation ratio of Ti is only about 25% at both 680 and 800 °C. The above dependence of nitridation ratio on annealing ambient is due to the difference in decomposition energy of gas molecules. The nitridation ratio increases on arsenic‐implanted Si because of a retardation effect of the arsenic on the silicidation reaction. The bilayer formation process was applied to the AlSi contact metallization on the n⁺ diffused layer. From measurements on electrical characteristics of the AlSi/TiN/TiSi₂/n⁺ Si contact system, the following results were obtained: (1) Contact resisitivity is 3.5–5.3×10⁻⁷ Ω cm². (2) The TiN/TiSi₂ contact electrode is thermally stable against Al. In particular, when the bilayer is formed in NH₃ at comparatively lower temperature, its thermal stability is still further improved. This is due to the formation of the thicker surface TiN layer.