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

氢从氢封端的Si衬底的电子刺激解吸（ESD）被期望用于与使用电子束图案化的表面改性有关的纳米制造中的多用途应用。在电子束图形化氢基片中，通常使用20-50 keV的高能电子束，电子束会引起氢的热脱附和ESD，为了抑制电子束的热效应，实现ESD引起的表面氢的局部去除，需要采用10 eV量级的超低能电子。为此，阐明超低能区ESD的机制具有重要意义。为了从原子尺度上阐明氢封端Si衬底的表面改性过程，本研究采用新引进的低能电子枪，利用飞行时间弹性反冲探测技术，对氢封端Si（100）和Ge/Si（100）表面的ESD过程进行了原位观测（TOF-ERDA），得到了超低能区氢的ESD截面与电子能量的关系。特别值得一提的是，我们在氢封端的Si（100）上的氢ESD机理上获得了有趣的发现;即，（1）ESD的阈值电子能量约为23 eV，和（2）ESD的机制与芯带激发有关，其中芯空穴的俄歇衰减发生在共价Si-H键中，导致成键轨道中的多空穴终态和H的脱附。

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.