Surface Modification of Hydrogen-Terminated Silicon Substrate using Extra-Low Energy Electron Beam

电子刺激解吸（ESD）从氢端硅衬底的氢有望在纳米制造中广泛应用，与使用电子束图案化的表面修饰有关。在端氢基板的电子束图案化中，通常使用20-50 keV的高能电子束，引起氢的热脱附和静电放电。为了抑制电子束的热效应，实现仅由ESD引起的表面氢的局部去除，需要采用10 eV级的超低能电子。为此，阐明超低能区静电放电的机理具有重要意义。本课题旨在从根本上阐明端氢Si衬底在原子尺度上的表面修饰过程。利用新引入的低能电子枪，利用飞行时间弹性后坐力检测分析（TOF-ERDA）对端氢Si（100）和Ge/Si（100）表面的氢气静电放电过程进行了原位观测，得到了氢气在超低能区静电放电截面的电子能量依赖关系。特别值得一提的是，我们从端氢Si中获得了关于氢静电放电机理的有趣发现（100）；即：(1)静电放电的阈值电子能约为23 eV；(2)静电放电的机制与核带激发有关，在核带激发中，共价Si-H键发生核心空穴的俄格衰变，导致键轨最终形成多空穴状态，H被解吸。

Electron-stimulated desorption (ESD) of hydrogen from hydrogen-terminated Si substrates is expected for versatile applications in nano-fabrication in connection with surface modifications with use of electron beam patterning. In the electron beam patterning of hydrogen-terminated substrates, e-beam with high energy of 20-50 keV is usually used, which causes thermal desorption of hydrogen as well as ESD.In order to suppress the thermal effect by e-beam and to realize local removal of surface hydrogen caused only by ESD, it is necessary to adopt extra-low energy electrons with 10 eV order. For this purpose, it is of great importance to elucidate the mechanism of ESD in the extra-low energy region. The purpose of this research project is to fundamentally elucidate the surface modification process of hydrogen-terminated Si substrates on atomic scale.With use of newly introduced low-energy electron gun, we performed in-situ observation of ESD processes of hydrogen from hydrogen-terminated Si(100) and Ge/Si( 100) surfaces using time-of-flight elastic recoil detection analysis (TOF-ERDA), and obtained the electron energy dependence of ESD cross-section of hydrogen in the extra-low energy region. The result worthy of special mention was that we obtained interesting findings on the mechanism of ESD of hydrogen from hydrogen-terminated Si(l00) ; namely, (1) threshold electron energy of ESD was about 23 eV, and (2) the mechanism of ESD was related to the core band excitation in which Auger decay of a core hole occurred in a covalent Si-H bond, leading to a multi-hole final state in the bonding orbital and desorption of H.