The Study On The Microstructure And Properties Of Al₂O₃ Thin Films Prepared By Radio Frequency Reactive Magnetron Sputtering

Aluminum oxide( Al₂O₃)thin films are widely used in mechanical, optical and microelectronic applications because of their excellent physical and chemical properties. Especially, Al2O3 thin films have very high hardness(up to 20³0 GPa) and very good thermal stability(melting point of α-Al2O3 is 2015℃). As a result, Al2O3 thin films may be coated on the devices as a protective coating to elongate their lifetimes and decrease the economic loss. At the present time, there are a lot of methods to prepare thin films and magnetron sputtering technique is more and more widely used to deposit all sorts of thin films due to its high sputtering velocity and low temperature. However, it is still a question how to determine sputtering process parameters, microstructure and properties of thin films.In this paper, Al2O3 thin films are successfully deposited by radio frequency (RF) reactive magnetron sputtering on silicon wafer and stainless-steel substrates. The properties of thin films are characterized in terms of x-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and micro-hardness tester and so on. The result shows that the deposition rates of Al2O3 thin films are dependent on the process parameters used such as radio frequency power, sputtering pressure, target-to-substrate distance, and oxygen flow rate;Al2O3 thin films deposited on room temperature are a typical amorphous and columnar structure;the oxygen/aluminum atomic ratio in the deposited film is in the vicinity of 1.50. With the increase of the substrate temperature, the deposition rate of Al2O3 thin films are very stable, the phase of thin films begins to transit from amorphous Al2O3 to γ-Al2O3 at deposition temperature of 500℃ , the roughness Rrms and Ra and micro-hardness of Al2O3 thin films increase continually.In addition, the different thickness aluminum oxide thin films deposited on stainless-steel substrates are annealed at 800 ℃ and 1000℃ for 6 hours, respectively. It is studied that the film thickness and annealing temperature have an influence on crystalline structure, surface morphology and micro-hardness of Al2O3 thin films annealed. The experimental results show that the film thickness has nearly influence on microstructure, while influence from the substrate on thefilm micro-hardness measured decreases with the increase of the film thickness. XRD shows that the process of phase transition of amorphous aluminum oxide thin film is a-Al2O3-> y-Al2O3 (majority) + a-Al2O3 (minority) +k-A12O3(800°C) ^a-Al2O3(majority)+y-Al2O3 (minority) + 5-Al2O3 + 0-Al2O3 +k-A12O3 (1000°C). Crystallization and density of films get better. The square roughness and micro-hardness of A12O3 thin films are increasing with the increase of annealing temperature. When the annealing temperature is 1000°C, micro-hardness of A12O3 thin film whose thickness is lOOOnm is up to 23GPa.