Ge/Si和TiN/Si₃N₄低维体系的表面和界面研究

【作者】 潘志云；

【导师】 韦世强；

【作者基本信息】 中国科学技术大学 ， 同步辐射及应用， 2006， 博士

【摘要】 本论文综合利用反射高能电子衍射（RHEED）、原子力显微镜（AFM）、高分辨透射电镜（HR-TEM）、Raman谱、X射线衍射（XRD）以及荧光X射线吸收精细结构（XAFS）等多种方法，研究Ⅳ-Ⅳ族Ge／Si低维半导体量子体系以及TiN／Si₃N₄超硬纳米多层膜的局域结构、表面和界面效应。利用RHEED和掠入射荧光XAFS方法研究Ⅳ-Ⅳ族二维半导体异质膜的厚度、形貌和原子局域结构，准确地测定具有金刚石结构的Ⅳ-Ⅳ族异质膜的组成以及四面体晶格扭曲等结构信息，分析Ge层和Ge-Si界面层的表面和界面效应，还结合AFM、HR-TEM以及Raman谱分析了零维量子点的形貌、发光特性和原子局域结构，有助于了解Ⅳ-Ⅳ族低维量子结构的形成机理，从而为Ⅳ-Ⅳ族低维量子体系半导体材料的设计制备提供指导。利用XRD和荧光XAFS技术研究TiN／Si₃N₄超硬纳米多层膜的长程结构和短程局域结构以及其界面效应，分析结构与性能的内在联系，为揭示高性能的TiN／Si₃N₄超硬多层膜体系的增硬机理提供结构基础。获得的主要研究成果如下： 1、Ge／Si低维量子体系 利用RHEED和掠入射荧光XAFS方法研究在400℃下分子束外延（MBE）生长的Ge_n／Si（001）单层膜（n=1～4 monolayer ML）和Si／Ge_n/Si（001）异质膜（n=1～8 ML）的形貌、Ge层厚度n及其对于Ge原子周围的局域结构的影响，研究在覆盖Si层的过程中所引起的Ge、Si原子间的相互作用，并探讨可能的界面作用机理。发现在所有的异质膜中都存在强烈的Ge原子向Si覆盖层迁移的效应，并且迁移长度较大：对于Ge原子层厚度仅为1 ML和2 ML的异质膜，几乎全部的Ge原子（0.5 ML和1.5 ML）都迁移进入了Si覆盖层而形成GeSi合金；随着Ge原子层的厚度增加到4 ML，第一近邻配位壳层中的Ge-Ge配位和Ge-Si配位的配位数(N_Ge-Ge:N_Ge-Si=2.7:1.3)近似于Ge_0.30Si_0.70合金膜的情况，大约有2ML的Ge原子与Si覆盖层混合；甚至对于Ge原子层厚度为8ML的异质膜，第一近邻配位壳层中的Ge-Ge配位占的比例只有55％，接近于Ge_0.50Si_0.50合金膜，并且有约3 ML的Ge原子迁移进入Si覆盖层。我们提出了Ge原子向Si原子表面迁移的机理，认为除了生长温度和生长速率的影响以外，Ge原子较Si原子具有更小的表面能是在Si覆盖层的生长过程中Ge原子发生表面偏析的主要原因之一，从而促使Ge原子向Si覆盖层迁移，并降低了Si覆盖层的表面能以及Ge层的应变能。更多还原

【Abstract】 In this thesis, the Reflection High Energy Electron Diffraction （RHEED）, Atomic Force Microscope （AFM）, high resolution Transmission Electron Microscope （HR-TEM）, Raman spectrum, X-ray Diffraction （XRD） and Fluorescence X-ray absorption fine structure （XAFS） have been synthetically used to study the local structures as well as the surface and interface effects of IV-IV semiconductors Ge-Si/Si（001） system and TiN/Si₃N₄ super-hard multilayer films. At first, the thickness, modality of Ge layer and local structures of IV-IV semiconductors hetero-structural films were investigated by RHEED and grazing incidence fluorescence XAFS. The composition and the structural parameters such as tetragonal unit cell distortion were accurately determined for the two-dimensional quantum semiconductors with diamond structure. The surface and interface effects of Ge layer and Ge-Si interlayer were analyzed in detail. Subsequently, the modality, optic characteristic and local structure of zero-dimensional quantum dots were studied through combining with AFM, HR-TEM Raman spectrum and XAFS techniques. Above investigation is useful to understand the formation mechanism of quantum structure in the Ge-Si quantum semiconductor system more reliably and straightforwardly and will provide new information on the design and fabrication of such system. Finally, XRD and Fluorescence XAFS were used to study the long order and local structure as well as the interface effect of TiN/Si₃N₄ super-hard multilayer films. The analysis on the intrinsic relationship between structure and performance will provide the structure foundation for explaining the hardness enhancement mechanism for TiN/Si₃N₄ super-hard multilayer films. The main content in this thesis is as follows:1. Ge/Si quantum systemThe RHEED and grazing incidence fluorescence XAFS has been used to study the thickness, modality of Ge layer and local structure of Ge_n/Si（001） （n=1, 2 and 4 monolayer, ML） overlayer and Si/Ge_n/Si（001） （n=1, 2, 4 and 8 ML） heterostructural films grown by MBE at 400℃. We investigated the interaction between Ge and Si atoms during the overgrowth of Si layer and discussed the possible mechanism of Ge-Si interface effect. The XAFS results indicate that there is a strong Ge migration effect in all Si/Gen/Si（001） heterostructural films and the length of migration is considerable. For the 1 or 2 monolayer （ML） Ge heterostructural film, the Ge atoms are dominantly surrounded by Si, and the Ge layers are completely consumed to form SiGe alloy. With the thickness of the Ge monolayer increasing to 4 ML, the determined Si/Ge coordination numbers (N_Ge-Si:N_Ge-Ge=2.7:1.3) is similar to that of Si_0.70Ge_0.30 alloy, and there are about 2.0 ML Ge atoms mixing with the Si capping layer. Even for the 8-ML-thick Ge heterostructural film, the fraction of Ge-Ge coordination pair in the first shell is about 55%, close to that in Si0.50Ge0.50 alloy. It means that about 3.0 nominal ML Ge atoms in Si/Ge₈/Si（001） heterostructural film migrate into the Si capping layer to form a Ge-Si alloy. We suggest the migration mechanism of更多还原