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

弄清金属表面氧化机理对稳定金属表面具有重要意义。然而，特别是在低温下，由于实验跟踪纳米级氧化的困难，实验结果很少。此外，纳米金属氧化物薄膜已被广泛应用于许多电子器件中。虽然它们的电学性质应该取决于氧化膜的质量，如偏离化学计量比组成引起的点缺陷、杂质、结构缺陷等，但目前还没有系统的研究。在本研究项目中，除了阐明铜的低温氧化过程外，还研究了杂质、结构缺陷和本征缺陷对纳米级氧化锆膜电学性能的影响，建立了控制纳米级氧化膜质量的指导方针。在315~378K，氧分压为0.1 Mpa的条件下，2N、4N和6N的氧化程度较高。用原位椭圆偏振光谱仪测量了氧化层厚度。结果表明，(100)晶面的氧化速率最高，而(110)晶面和(111)晶面的氧化速率相近。在多晶情况下，6 N-铜的氧化速度最快。结果表明，低温氧化动力学在5 nm以下符合反对数规律，在5~25 nm范围内符合三次曲线规律，在25 nm以上符合抛物线规律。采用负偏压离子束沉积系统(IBD)制备纯锆膜，在0.1MPaO_2气氛下473 K氧化60min两步法制备了氧化锆薄膜，并研究了锆膜质量对氧化膜电学性能的影响。为了弄清纯度和结构缺陷的影响，采用提纯的锆靶，在-50V的负衬底偏压下，采用离子束沉积的方法在铂/硅或硅衬底上沉积了锆膜。为了控制自然氧化物的浓度，在紫外光(λ=193 nm，深紫外灯)照射和不照射的情况下对锆膜进行了氧化处理。用X射线衍射仪、扫描电子显微镜、高分辨电子显微镜和X射线光电子能谱对薄膜进行了表征。电容-电压(C-V)和电流-电压(I-V)测量采用MIM结构或MOS结构。研究发现，杂质、结构缺陷和本征缺陷的减少显著提高了介电常数，降低了漏电流。较少

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