Thermal stability of electrode stacks for application in oxide film devices

摘要

Different bottom electrode stacks have been successfully produced by (r.f.) magnetron (reactive) sputtering and UHV electron beam evaporation, respectively. The effects of post-annealing in oxygen ambient on the microstructure, surface morphology, surface roughness, and resistivity of the stacks were investigated. It was found that zirconia (ZrO2), titanium oxide (TiO2) and silica (SiO2) interlayers were stable and remained well defined after high temperature annealing. Pt/TiO2/ZrO2/Si and Pt/TiO2/SiO2/Si bottom electrode stacks have smooth and continuous surface morphology after annealing at 800 °C for 30 min. These thermally stable bottom electrode stacks have lower resistivity than other stacks which is desirable for improving ferroelectric thin film electric properties. Because the Ti and Si3N4 interlayers are not thermally stable, the Pt/Ti/SiO2/Si and Pt/TiO2/Si3N4/SiO2/Si bottom electrode stacks became porous after annealing at 800 °C for 30 min. Because Ti diffusion through Pt can enhance the Pt grain growth, the Pt/Ti/SiO2/Si stack has the largest grain size compared with other stacks after being subjected to the same annealing temperature. In the Pt/TiO2/Si stack, the surface morphologies change significantly with different annealing temperature, which indicates that using SiO2 as a barrier layer is essential and this layer cannot be replaced by TiO2.