Properties of iridium-inserted nickel silicides by thermal annealing of the Ni/Ir bilayer on silicon and polysilicon substrates

Abstract

To improve the thermal stability of the conventional nickel monosilicide, 10 nm-Ni/l nm-Ir/p-Si(100) (or poly-crystalline Si) was thermally annealed using rapid thermal annealing for 40 s at 300–1200°C. The annealed bilayer structure developed into Ni(Ir)Si, 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 Ni(Ir)Six formed on single crystal silicon was approximately 40 nm, and it maintained a sheet resistance of below 20 ω/sq. during the silicidation annealing at 1200°C. The silicide formed on polysilicon had a thickness of 55 nm, and its low resistance was maintained up to 850°C. An additional annealing of silicides at 900°C for 30 min. resulted in a drastic increase in sheet resistance. A possible reason for the improved thermal stability of the silicides formed on single crystal silicion substrate is the role of iridium in preventing NiSi2 transformation. Iridium also improved the thermal stability of the silicides formed on the polysilicon gate, but this enhancement was lessened due to the formation of NiIrSix and also as a result of silicon mixing during high temperature diffusion. In conclusion, the proposed iridium-inserted nickel silicides may be superior to the conventional nickel monosilicides due to improved thermal stability.