Effects of UV-ozone treatment on radio-frequency magnetron sputtered ZnO thin films

• Published in: Thin solid films Vol. 520; no. 1; pp. 569 - 573
• Main Authors: Tang, W.M., Greiner, M.T., Lu, Z.H., Ng, W.T., Nam, H.G.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 31.10.2011; Elsevier
• Subjects: Applied sciences; Capacitors; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Density; Deposition by sputtering; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronics; Exact sciences and technology; Fermi surfaces; Materials science; Metal oxide semiconductors; Metal-oxide-semiconductor capacitor; Methods of deposition of films and coatings; film growth and epitaxy; Ozone; Photoelectron spectroscopy; Physics; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Surface and interface electron states; Surface double layers, schottky barriers, and work functions; Surface states, band structure, electron density of states; Thin films; Threshold voltage; Transistors; UV-ozone treatment; X-ray photoelectron spectroscopy; Zinc oxide; Thin films; Metal-oxide-semiconductor capacitor; Zinc oxide; Threshold voltage; X-ray photoelectron spectroscopy; UV-ozone treatment; Voltage threshold; Work functions; Vacancies; Semiconductor materials; Hafnium oxide; Thin film transistors; Leakage currents; CV characteristic; Breakdown voltage; Electronic structure; Fermi level; MOS capacitors; Physical vapor deposition; Ultraviolet photoelectron spectra; Radiofrequency sputtering; X-ray photoelectron spectra
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2011.07.004

The effects of UV-ozone treatment on ZnO thin films prepared by using radio-frequency magnetron sputtering are investigated. Decrease in the density of oxygen vacancy as well as increase in the density of oxygen interstitial were inferred from the UV-ozone treated samples. It was also found that a considerable difference in the work function (0.25 eV) is induced by UV-ozone treatment implying a shift in Fermi level. This shift was confirmed by capacitance–voltage measurements, which demonstrated that the boundary between the inversion region and the depletion region of a ZnO-based metal-oxide-semiconductor (MOS) capacitor positively shifts when UV ozone treated. Our results clearly indicate that the threshold voltage of a thin film transistor can be adjusted by modifying the ZnO surface via UV ozone treatment. MOS capacitors fabricated with UV-ozone treated HfO 2 and/or ZnO also yielded a smaller leakage current (~ 73%–90% smaller) and a larger breakdown voltage (~ 8%–11% larger). The physical mechanism behind the effect of the UV ozone treatment is addressed in this study with the help of X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy.