Study of vacancy-type defects in metal/metal-oxide by means of positron annihilation

研究项目的测量目标是研究金属氧化物中的空位型缺陷（特别是氧空位）以及金属/金属-氧化物界面形成所引入的原子和空位的扩散。对热氧化法制备SiO_2/Si和金属/SrTiO_3结构进行了表征。结果表明，在SiO_2薄膜上沉积Al会降低SiO_2/Si的电学性能。利用单能正电子束流，在Al沉积过程中引入电子或空穴陷阱，这些陷阱捕获正电子或激发电子，从而抑制了正电子离子（Ps）的形成概率。本研究中所研究的MOS结构电性能的退化主要是由于氧原子在Al膜中的扩散。在Si衬底上沉积HfO_2和HfON薄膜，并沉积TiN形成MOS结构。对湮灭辐射的多普勒展宽谱和正电子的寿命谱的测量表明，正电子在薄膜的非晶结构中被固有的开放体积湮灭。通过对数据的分析，发现在高硅界面附近存在负电荷。在CVD沉积TiN薄膜时，观察到Si衬底的电场没有大的变化。然而，当使用PVD沉积薄膜时，正电子从界面被排斥，这表明通过形成氧空位引入了正电荷。我们证实了正电子湮没参数对金属/氧化物-金属结构的缺陷非常敏感，可以作为研究金属/氧化物-金属界面的潜在工具。

The measure target of the research project is the study of vacancy-type defects (especially oxygen vacancies) in metal oxides and the diffusion of atoms and vacancies introduced by the formation of metal/metal-oxide interface.SiO_2/Si fabricated by thermal oxidation and metal/SrTiO_3 structures were characterized. It was found that the electrical properties of SiO_2/Si were degraded by the deposition of Al on SiO_2 films. By using monoenergetic positron beams, electron or hole traps were introduced by the Al deposition and as a results the formation probability of positronium (Ps) was suppressed by the trapping of positron or spur electrons by such traps. The degradation of the electrical properties of MOS structures investigated in the present study is mainly due to the diffusion of oxygen atoms into Al films.HfO_2 and HfON thin films were deposited on Si substrates and TiN was deposited to form MOS structures. Measurements of the Doppler broadening spectra of annihilation radiation and the lifetime spectra of positrons indicated that positrons annihilated from the trapped state by open volumes that exist intrinsically in amorphous structures of the films. From the analysis of the data, negative charges were found to present near the high/Si interface. When the TiN films were deposited using CVD, no large change in the electric field in the Si substrate was observed. When the films were deposited using PVD, however, positron were repelled from the interfaces, suggesting the introduction of positive charges by the formation of oxygen vacancies.We confirmed that the positron annihilation parameter is sensitive to the defects in metal/oxide-metal structure, and it can be used to potential tool for the investigation of metal/oxide-metal interface.