Properties of nickel-cobalt composite silicides by thermal annealing of Ni_1-xCo_x(x = 0.2, 0.5, and 0.8) alloy thin films on silicon and polysilicon substrates

10 nm-Ni_1-xCo_x (x = 0.2, 0.5, and 0.8) /p-Si(100)(or poly crystalline Si) was thermally annealed using rapid thermal annealing for 40 s at 600-1100°C. The annealed film structures developed into NiCoSi _x, and the resulting changes in sheet resistance, microstructure, and composition were investigated using a four-point probe, a scanning electron microscope, a field ion beam, an X-ray diffractometer, and an Auger electron spectroscope. The final thickness of NiCoSi_x formed on single-crystal silicon was approximately 12.64 nm, and it maintained its sheet resistance below 20 Ω/sq. during the silicidation annealing at 1100°C. The NiCoSi_x formed on polysilicon had a thickness of 35.04 nm, and its low resistance was maintained up to 900°C. Additional annealing of suicides at the given RTA temperature for 30 min resulted in a drastic increase in sheet resistance. We identified Ni₃Si₂ and a NiSi phase at 700°C and 1000°C for single-crystal silicon substrates. Moreover, Ni₃Si₂, NiSi, and CoSi₂ phases were stable at 700°C, and then NiSi₂ and Ni₃Si₂ became stable for polycrystalline silicon substrates at 1000°C. When the amount of Co was 80 %, only a Ni₃Si₂ phase was confirmed at 700°C and 1000°C in both the single and polycrystalline substrates. With less Co (Co = 0.2, 0.5), Ni₃Si₂, NiSi, and CoSi ₂ phases were observed at 700, and Ni₃Si₂ and NiSi₂ phases were observed at 1000°C. Cobalt also improved thermal stability of the suicides formed on the polysilicon gate, but this enhancement was lessened due to the silicon mixing during high temperature diffusion. In conclusion, the proposed nickel cobalt composite silicides formed from the nano-thick alloy films may be superior to conventional nickel monosilicides due to improved thermal stability.