Preparation and properties of dc-sputtered IrO2 and Ir thin films for oxygen barrier applications in advanced memory technology

Abstract

IrO 2 and Ir thin films have been deposited by dc sputtering in Ar/O2- and pure Ar atmospheres, respectively. The microstructural characterization of the films was done by x-ray diffraction and transmission electron microscopy and showed that (nano-)crystalline Ir and IrO2 films with different textures could be deposited. Stress analyses showed that the stress of the Ir films can be varied from about −3.5 GPa for a deposition temperature of 100 °C to nearly zero stress if deposited at 500 °C. However, IrO2 films generally exhibited a large compressive stress of about −1.5 GPa, which is nearly independent of substrate temperature, but changed with texture and stoichiometry of the films. Surface and roughness analyses of the cumulatively annealed samples were performed by various analysis methods, and stoichiometry was examined by Rutherford backscattering spectrometry. In situ stress measurements were used to investigate the stress relaxation behavior of the films up to 900 °C. We demonstrate that it is generally possible to optimize reactive IrO2 sputter deposition by a detailed study of plasma and deposition conditions via recording generic curves for the sputtering system used. At optimized conditions these fine grained IrO2 films exhibit very high thermal phase stability to at least 800 °C for several hours and a very low roughness. The aim of these investigations is to optimize stability of IrO2 films under high temperature conditions for oxygen barrier application in dynamic random access memory and nonvolatile Fe random access memory cells.