Mechanical properties of HfO₂-SiO₂ mixed films

Six groups of HfO2-SiO2 mixed films with SiO2 content about 0, 13%, 20%, 30%, 40% and 100% were prepared using ion-assisted e-beam co-evaporation process separately. The Young's modulus and hardness of the mixed films with different SiO2 content were measured through nanoindentation, and the variation of Young's modulus and hardness as a function of SiO2 content were studied. The results show that with the increase of SiO2 content, both the Young's modulus and hardness of the mixed films decrease, and the variation of Young's modulus of mixed films as a function of SiO2 content can be well fitted by iso-stress model of a two-component composite. In order to illustrate the relation between SiO2 content and mechanical properties of the mixed films, the microstructure of the mixed films was analyzed by XRD, and the influence of microstructure on Young's modulus and hardness were studied. It was found that the crystallization of thin films had major impact on hardness, but little influence on Young's modulus. The residual stresses of the mixed films were calculated using the data of surface shape measured by Zygo interferometer, the variation of stress as a function of SiO2 content was obtained, and a reduction of compressive stress with the SiO2 doped in HfO2 was observed.