Surface chemistry of hydrogen on Si surfaces

为了从原子/分子的角度阐明硅外延的生长机理，我们完成了以下工作。我们发现，在Si- gsmbe中，源气体分子在低温下通过两个位点和高温下通过四个位点吸附在Si表面。阐明了低温下决定生长速率活化能的机理。首次阐明了Si（100）表面的氢脱附可以发生大于单位的反应级数，这与以往的认识不同。反应顺序取决于加氢气体的选择和热历史，热历史的变化可以用表面成对氢原子的浓度来统一解释。对于原位掺杂过程中的表面化学，我们首先开发了一种控制磷原子表面覆盖的新方法，即简单地计算吸附/解吸序列的数量。利用该方法，发现表面P原子在Si外延上的作用是抑制吸附过程和抑制氢的脱附。更准确地说，后一种效应包括两个渠道：活化能的增加和反应级数的提高。这些发现为了解磷掺杂对生长速率的影响提供了依据。为了在硅表面实现良好的SiC异质外延，我们比较了乙炔和单甲基硅烷（MMS）吸附硅表面的原子排列。在乙炔吸附表面，表面碳原子与衬底Si原子之间发生位点交换，而在mms吸附表面，这种交换被明显抑制。然后，通过MMS，在Si（100）上成功地获得了合格的SiC晶体膜，温度低至900℃，没有任何碳化过程。阐明了表面氢的完全消除是SiC外延合格的关键。

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.