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

研究对象是金属氧化物中的空位型缺陷(尤其是氧空位)，以及金属/金属-氧化物界面形成过程中原子和空位的扩散。研究发现，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，铝沉积引入了电子或空穴陷阱，从而抑制了正电子或杂散电子的形成几率。本文研究的MOS结构的电学性能劣化主要是由于氧原子向Al薄膜的扩散。在Si衬底上沉积了HfO2和HfON薄膜，在TiN上沉积了MOS结构。湮没辐射的多普勒展宽谱和正电子寿命谱的测量表明，正电子被薄膜非晶态结构中固有的开放体积从俘获态湮没。通过对数据的分析，发现在高/硅界面附近存在负电荷。用化学气相沉积方法沉积TiN薄膜时，Si衬底上的电场变化不大。然而，当用PVD沉积薄膜时，正电子从界面上被排斥，这表明正电子通过形成氧空位而引入正电荷。我们证实了正电子湮没参数对金属/氧化物-金属结构中的缺陷很敏感，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.