Stoichiometry Control of ZnO Thin Film by Adjusting Working Gas Ratio during Radio Frequency Magnetron Sputtering

ZnO thin films were deposited on quartz glasses by a radio frequency (rf) magnetron sputtering. The mechanism for stoichiometry in the ZnO thin films was investigated by adjusting Ar/O2 working gas ratio during deposition. The optical emission spectroscopy (OES) in situ measurement revealed the kinetics species variation during rf plasma deposition process. It was found that the intensity of the excited atomic oxygen (O*) was increased with the oxygen ratio increasing, resulting in enhancing the oxidization effect during ZnO film fabrication. On the contrary, the intensities of atomic zinc emission were gradually decreased, resulting in the zinc ratio in the film were decreased with the oxygen ratio increasing. Therefore, it is possible to control the stoichiometry of ZnO film by simply adjusting the working gas ambient in the rf plasma deposition. The structural and optical properties of ZnO thin films were investigated as well. 1. Introduction In recent years zinc oxide (ZnO) thin films, a compound semiconductor material with a wide-band gap of (3.37？eV at 300？K), have attracted much attention for applying in different photonic and electronic devices such as optical waveguides, thin film transistor, and gas sensors [1–3], due to its promising electrical, optical, and piezoelectric properties. Among the many fabrication techniques of ZnO film, radio frequency (rf) magnetron sputtering is considered as a convenient method for deposition of homogeneous ZnO thin film on large area because the stability and reproducibility of ZnO films are quite high comparing to other techniques [4]. In our previously work [3, 5], some optimum deposition conditions using rf magnetron sputtering system had been found to prepare high-quality ZnO films for TFTs application. We already found that the bombardment effect of energetic particles during rf magnetron sputtering was one of the important factors influencing the properties of ZnO thin films [6]. Comparing to a low-pressure deposition [7], we found that the properties of as-deposited ZnO thin films were changed by a high-pressure deposition procedure. However, the structural and optical properties of ZnO films obtained from high-pressure deposition process were still not quite understood. In this research, the effects of different working gas (Ar/O2) ratios on the fabrication of ZnO films were investigated under a high deposition pressure of 7？Pa. The mechanism for ZnO film stoichiometry was discussed, and the structural and optical properties of ZnO films were evaluated. The experiment result is expected to supply