Amorphous CoTix as a liner/diffusion barrier material for advanced copper metallization

This paper reports the possibility of using an amorphous Co-Ti alloy as a single-layer liner/barrier material for multilayer Cu interconnects in advanced silicon devices. Theoretical and experimental results both showed a stable composition range of an amorphous phase at room temperature to be Co-18 to 83 at% Ti. Liner/barrier property was investigated using sputtered films of Cu (150 nm)/CoTix (3 nm) on thermal SiO2/p-Si substrates, where x = 25 ± 3 at%Ti. The CoTix layer was found to enhance adhesion between Cu and SiO2. The CoTix layer stayed amorphous after annealing at 400 °C, and started to crystallize at 500 °C. The crystallization accompanied the dissociation of CoTix, leading to the formation of Ti oxide and Cu-Co solid solution. Capacitance-voltage measurement of the samples showed no interdiffusion of Cu ions into SiO2 after annealing at 600 °C and after bias temperature annealing at 250 °C at 3 MV/cm. The results indicated that the CoTix alloy would be a good candidate for a single-layer liner/barrier material to replace a double-layer Ta/TaN.