High-temperature X-ray scattering studies of atomic layer deposited IrO₂

IrO₂ is an important material in numerous applications ranging from catalysis to the microelectronics industry, but despite this its behaviour upon annealing under different conditions has not yet been thoroughly studied. This work provides a detailed investigation of the annealing of IrO₂ thin films using in situ high-temperature X-ray diffraction and X-ray reflectivity (HTXRR) measurements from room temperature up to 1000°C in oxygen, nitro­gen, forming gas and vacuum. Complementary ex situ scanning electron microscopy and atomic force microscopy measurements were conducted. The combined data show the dependencies of crystalline properties and surface morphology on the annealing temperature and atmosphere. The reduction of IrO₂ to Ir takes place at a temperature as low as 150°C in forming gas, but in oxygen IrO₂ is stable up to 800°C and evaporates as a volatile oxide at higher temperatures. The IrO₂ crystallite size remains constant in oxygen up to 400°C and increases above that, while in the more reducing atmospheres the Ir crystallites grow continuously above the phase-change temperature. The role of HTXRR in the analysis is shown to be important since its high sensitivity allows one to observe changes taking place in the film at temperatures much below the phase change.