Thermal stability of metal electrodes (Pt, Ru, & Ir) on polycrystalline silicon in ferroelectric capacitors

Electrode materials such as Pt, Ru, and Ir on polycrystalline silicon were annealed and the thermal stability was investigated to check the feasibility of the structure. Sputtered Pt reacted with silicon to form PtSi at a low temperature of 400 °C and the top layer of silicide was oxidized in oxygen ambient. Ru and Ir films by sputtering were also silicidized above 550 °C and it made voids beneath silicide layers. All of the films are found to allow oxygen to diffuse through them and to get the underlying layers oxidized. However, Ir deposited by e-beam evaporation did not form silicide up to 700 °C and did not get oxidized up to 550 °C. Ir also allowed oxygen diffusion when annealed at 550 °C or lower temperature, but it was prevented when annealed at 700 °C.