ALD Zirconium Oxide (ZrO 2 ) Thin Films Mechanical/Structural Properties for High-Tech Applications

Abstract

The nanomechanical and structural properties of atomic layer deposition (ALD) zirconium oxide (ZrO 2) films of varying thickness deposited on p-type Si (100) substrates with 200, 300, and 500, ALD deposition cycles were investigated. The 300 ALD deposition cycles ZrO 2 films were further annealed at 600 • C. The nanomechanical properties of the films were tested using nanoindentation and the surface morphology was investigated using AFM. The structural and surface properties were explored using field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). We discuss the influence of the deposition technique on the structure and properties of the ZrO 2 films resulting from ALD synthesis. The nanoindentation results indicate that the films become consistently softer as the number of ALD deposition cycles increase and the film grows thicker. Further annealing of the films at 600 • C slightly enhanced the hardness and fracture toughness of the films. The annealed ALD films depicted shorter radial cracks compared to the films under the same applied stress, which were not annealed in forming gas. Among the transition metal oxides, zirconium oxide (zirconia) ZrO 2 is considered the most extensively studied because of its re-markable properties such as high melting point, resistance against oxidation, and high refractive index. 1–3 Monoclinic crystal structure exists at room temperature and in the temperature range of up to 1170 • C, whereas in the temperature range of 1170–2370 • C the domi-nant crystal structure is tetragonal. As the temperature increases above 2370 • C and up to 2680 • C, the crystal structure becomes cubic. Zirco-nia is one of the hardest ceramics known and the predominant large volume application for ZrO 2 today is actually mostly ceramics pro-duction. One the special products is ceramic knifes made of zirconia, which last longer than steel knifes. Due to these various properties, zirconium oxides have been used in protective coatings, optical de-vices, laser mirrors, biomedical and in microelectronic applications. ZrO 2 is being used in artificial hip joints replacements due to its exceptional hardness and excellent mechanical properties and in den-tal implants, dental crowns and bridges due to its hardness and its good resistance to bacterial infection. Zirconium oxide also possesses high refractive index and high transparency in the visible and near-infrared region making it one of the most desirable materials for optical devices. 4