Pt hillock formation and decay

The formation of Pt hillocks during high temperature processing is a problem when using Pt as a bottom electrode for high dielectric constant materials. The hillock height is frequently larger than the dielectric thickness, degrading the leakage current of the device. In this work, Pt was deposited by electron beam evaporation on in-situ formed 40 nm ZrO₂ coated SiO₂/Si substrates. The samples were then annealed at temperatures between 400 °C and 700 °C for times ranging from 2 min to 40 min. The surface roughness was measured by atomic force microscopy (AFM). The surface was characterized using Ra, RMS and Zmax over 5 μm×5 μm regions. Zmax is sensitive to hillock formation and Ra is sensitive to changes in general surface roughness. Analysis of Zmax indicates that 100 nm Pt/ZrO₂ deposited at 315 °C forms hillocks above 450 °C during initial heatup. Subsequently, the hillocks decay for temperatures of 600 °C and above such that they are almost gone after a 30 min air anneal. In-situ wafer stress measurements of Pt/ZrO₂ were performed in O₂ at temperatures up to 650 °C. The Pt relaxes above 500 °C in O₂.