Buried, self-aligned barrier layer structures for perovskite-based memory devices comprising Pt or Ir bottom electrodes on silicon-contributing substrates

Abstract

The integration of noble metal electrodes into semiconductor memory devices incorporating ferroelectric or high dielectric constant ε materials is expected to require deposition of a conductive, oxidation-resistant barrier material between the noble metal and the silicon contact. Described is an alternative type of barrier layer structure which is formed as buried, self-aligned layer during oxygen-ambient annealing after noble metal deposition on silicon-contributing substrates. Reactions of Pt(20 nm) and Ir(20 nm) films with substrates of single crystalline silicon (c-Si), polycrystaline silicon (poly-Si), and tungsten silicide (WSix/Si with x=2.4–2.8) were examined after anneals in atmospheric pressure ambients of oxygen or nitrogen at temperatures of 640–700 °C, a temperature range of interest for high-epsilon materials deposition. While Pt(20 nm) films reacted with silicon and WSix/Si during oxygen annealing to form a mixture of Pt silicides and Pt, Ir(20 nm) films on the same substrates did not form any iridium silicides during oxygen annealing. In all cases, unreacted noble metal M was left due to the formation of an oxygen-containing M–O–Si barrier which interfered with the silicidation reaction. In contrast to these results for oxygen annealing, the Pt and Ir films were completely consumed by silicidation reactions during anneals in nitrogen. Qualitative through-film resistance measurements indicated that the M–O–Si barrier layers formed during oxygen annealing were at least moderately conductive for the cases of M=Ir on silicon and M=Ir or Pt on WSi2.8(300 nm)/Si, a prerequisite for the use of these electrode barrier structures in high-density dynamic random access memory.