Surface chemistry of hydrogen on Si surfaces

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With an aim of clarifying the growth mechanism of Si epitaxy on atomic/molecular basis, we have achieved the following.1. We found that, in Si-GSMBE, source-gas molecules adsorb onto the Si surface using two sites at low temperatures and four sites at high temperatures. The mechanism that determines the growth-rate activation energy at low temperatures was also clarified.2. It was clarified for the first time that hydrogen desorption from Si(100) surface can take a reaction order that is larger than unity, as opposed to previous understandings. The reaction order depends on the choice of the hydrogenating gas and the thermal history, whose variation is unifiedly accounted for by using a concentration of paired hydrogen atoms on the surface.3. Concerning the surface chemistry during in-situ doping process, we first developed a novel method for controlling the surface coverage of phosphorus atoms, in which we simply count the number of adsorption/desorption sequence. Using the method, the role of surface P atoms on Si epitaxy was found to be suppression of the adsorption process and suppression of the hydrogen desorption. More precisely, the latter effect consists of two channels : increase of the activation energy and the increase of the reaction order. These findings provide basis for understanding the growth-rate retardation during phosphorus doping.4. To achieve good SiC heteroepitaxy on Si, we compared the atomic arrangements of acetylene- and monomethylsilane(MMS)-adsorbed Si surfaces. On acetylene-adsorbed surface, there occurs site exchange between surface carbon and substrate Si atoms, while the exchange is drastically suppressed on MMS-adsorbed surface. By using MMS, then, a qualified crystalline film of SiC was successfully obtained on Si(100), at as low as 900C without any carbonization procedures. It was clarified that complete elimination of surface hydrogen is key to the qualified epitaxy of SiC.