Low Temperature Oxidation of Ultra-High Purity Metals and Stoichiometry Control of Oxide Films

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To clarify the mechanism of surface oxidation of metals is very important to stabilize the metal surface. However, especially, at low temperatures, experimental result is few because of the difficulty of experiments to follow the nano-scale oxidation. Furthermore, nano-scale metal oxide films have been used widely in many electronic devises. Although their electrical properties should be dependent on the quality of the oxide film, such as point defects caused by the deviation from the stoichiometric composition, impurities, structural defects, and so on, there has been no systematic study. In this research project, the effects of impurities, structural defects and native defects on the electrical properties of nano-scale Zr oxide films in addition to clarifying the low temperature oxidation of Cu to establish the guideline to control the quality of nano-scale oxide films.Single-crystal-copper ((100), (110), (111)) with the purity of 5N and poly-crystal copper specimens with different p … More urities of 2 N, 4 N and 6 N were oxidized at 315 ~ 378 K under 0.1 MPa of oxygen partial pressure. The oxide thickness was measured by in-situ spectroscopic ellipsometry. It was confirmed that oxidation rate of (100) was the highest, and those of (110) and (111) were similar. In the case of poly-crystal, the oxidation of 6 N-copper was the fastest. It is found that the low temperature oxidation kinetics were the inverse-logarithmic law below 5 nm, the cubic law from 5 nm to 25 nm and the parabolic law over 25 nm. In addition the activation energy was estimated and the similar value to that in Cabrera-Mott theory was obtained.ZrO_2 layers were prepared using a two-step method, i.e., fabrication of pure Zr films by negatively biased ion beam deposition system (IBD), and oxidation of pure Zr films at 473 K for 60 min under 0.1 Mpa O_2 atmosphere, and the effect of Zr film quality on the electrical properties of ZrO_2 layer was investigated. In order to to clarify the influence of purity and structural defects, the purified Zr target was used and Zr films were deposited on the Pt/Si or Si substrate by means of ion beam deposition with applying the negative substrate bias voltage of - 50V. To control the native oxide concentration, Zr films were oxidized with/without UV light irradiation (λ=193 nm, Deep UV lamp). Characterization of Zr and ZrO_2 films were carried out using XRD, FE-SEM, HRTEM and XPS. Capacitance-voltage (C-V) and current-voltage (I-V) measurements were carried out using MIM structure or MOS structure. It was found that the decrease of impurity, the structural defects and the native defects remarkably increase the dielectric constant and decrease the leakage current. Less