Studies on Surface Reaction Mechanisms in Atomic Layr CVD by HREELS

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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