Noble metal suicide formation in metal/Si structures during oxygen annealing: Implications for perovskite-based memory devices

This paper investigates the potentially undesirable noble metal silicide formation reactions that may occur in noble metal electrodes deposited directly on silicon without an intervening diffusion barrier. Metal (90-100 nm)/Si structures of Pt/Si, Rh/Si, Ir/Si, and Ir/Ti/Si were annealed in oxygen or nitrogen ambients at temperatures of 640-700°C. Metal/silicon reactions and phase formation were studied by Rutherford Backscattering Spectroscopy, x-ray diffraction, and electrical resistance measurements. While complete silicidation was observed in the Rh/Si, Pt/Si, and Ir/Si samples after 640°C/6 min anneals in nitrogen, some Pt and most of the Ir remained after equivalent anneals in oxygen. More detailed studies of the Ir/Si samples indicated that some Ir is left unsilicided even after a 700°C/6 min anneal in O2, and that the iridium silicide formed is the semiconducting IrSi1.75. The formation of this suicide can be delayed, but not prevented, with the use of a 5 nm Ti adhesion layer between the Ir and Si.