RF magnetron-sputtered ZNO thin films: on the evolution of microstructure and residual stresses

Official URL: http://risc01.sabanciuniv.edu/record=b1221510 (Table of Contents)

Thin ZnO films (200-500 nm) were deposited onto glass, mica, and Si(100) substrates, to study the relations between microstructure and residual stresses. The ranges for the substrate temperature, chamber pressure, and RF power were room temperature-200 °C, 0.009-0.4 mbar, and 100-125 W, respectively. The strain measurements by x-ray diffraction and the biaxial stress model showed that the films were under residual compressive stresses from -2 to -8 GPa. 5-11 percent of those stresses were induced by the thermal expansion coefficient mismatch, while the so-called growth stresses formed the majority. The films were strongly textured along the (002)-direction with additional (lOl)-texture under specific conditions. The texture of the film-substrate interface played a significant role in the average film texture and the residual stress. Variations from the previously developed structure zone models (SZM) and the microstructures in the pressure ranges beyond those SZMs were investigated by scanning electron microscopy. Several mechanisms of microstructure evolution and consequent stress development were proposed. Thermal annealing and aging removed the growth stresses and improved the texture. Annealing caused pore clustering and crack formation. Thus, annealing should be treated with caution when used as a method for stress relaxation. Buffer layer deposition and in-chamber heat treatment were proposed as alternatives to post-deposition annealing.Annealing led to structures on the ZnO film surface up to 100 nanometers in width and 1 micrometer in height. This was attributed to the stress-induced directional diffusion.