Studies on Surface Reaction Mechanisms in Atomic Layr CVD by HREELS

利用高分辨电子能量损失谱(HREELS)和反射高能电子衍射(RHEED)研究了氢原子对Si2H6和GeH4源分子束外延生长SiGe薄膜的初始氧化过程、SiO2的局域成键结构和外延生长过程的影响。主要结果如下：我们将随机顺序吸附模型应用于H-端基Si(100)表面初始氧化的实验结果。研究发现，氧原子优先吸附在表面硅原子的两个背键位置中的一个位置上，该位置位于H-端的Si(100)表面-Lx1和-2x1表面。在清洁的Si(100)表面上没有观察到氧原子的优先吸附，这意味着这一发现表明氢在一定程度上控制了氧化。此外，还清楚地表明，在表面硅的所有背键位都达到…之前，氧化态几乎不会进入硅衬底更多的被氧原子占据。这表明氢对实现SiO_2/Si界面的突变是有效的。在H端Si(111)-LX1表面的初始氧化过程中，氧原子随机吸附在表面和亚表面硅原子之间的位置上，氧覆盖率低于2.5单分子层(ML)。在Si(100)和Si(L11)表面上的SiGe外延生长中发现，Si_2H_6和GeH_4的解离吸附速率显著地依赖于表面取向和吸附位置的原子元素。这表明Si2H6和GeH4分子的表面反应是由衬底表面的电子态决定的。氢原子辐照对SiGe薄膜生长速率的影响主要是降低了氢化物气体的吸附位置密度，抑制了Ge原子的表面偏析。这些结果支持了氢气控制表面反应的实现。较少

In this study, we have investigated the effects of hydrogen atoms on the initial oxidation process, the local bonding structure of SiO 2 and the epitaxial growth process of SiGe films by Si_2H_6- and GeH_4-source molecular beam epitaxy, using high-resolution electron energy loss spectroscopy (HREELS) and reflection high energy electron diffraction (RHEED) . The main results are shown below.We applied a random sequential adsorption model to the experimental results of the initial oxidation on H-terminated Si (100) surfaces. It was found out that oxygen atoms preferentially adsorb on one of two back-bond sites of a surface Si atom on H-terminated Si (lO0) - lx1 and -2x1 surfaces. The preferential adsorption of oxygen atoms cannot be observed on clean Si (100) surfaces, which means that this finding shows something of the oxidation control by hydrogen. Moreover, it was also made clear that the oxidaton hardly progresses into the Si substrate until all back-bond sites of surface Si aotms a … More re occupied by oxygen atoms. This shows that hydrogen is effective for the realization of an abrupt SiO_2/Si interface.In the initial oxidation process of H-terminated Si (111) - lx1 surfaces, oxygen atoms randomly adsorb on the sites between surface and subsurface Si atoms below an oxygen coverage of 2.5 monolayer (ML) . In addition, we clarified that the local bonding structure of Si-O-Si species is hardly influenced by the orientaion of Si substrartes and by the adsorbing hydrogen atom.It was found in the SiGe epitaxial growth on Si (100) and Si (l11) surfaces that the dissociative adsorption rates of Si _2H_6 and GeH _4 are significantly dependent upon the surface orientation and the atomic element at the adsorption sites. This suggests that the surface reactions of Si_2H_6 and GeH_4 molecules are ruled by the electronic states of the substrate surface. The role of atomic hydrogen irradiation in the growth rate of SiGe films is to reduce the density of adsorption sites for the hydride gases and to suppress the surface segregation of Ge atoms. These findings support the realizaiton of the surface reaction control with hydrogen. Less