A study on influences of hydrogen on growth mechanisms of thin films by electron energy loss spectroscopy

我们利用高分辨率电子能量损失谱和反射高能电子衍射研究了薄膜的外延和氧化等生长过程。特别是氢，因为它在生长过程中起着重要的作用，一直受到我们的关注。因此，我们利用Si_2H_6研究了氢对Ge/Si外延生长的影响，得到的主要结果如下：1)在低于550℃的温度下，Si在Si（100）表面生长，其生长速率的活化能与Si（100）表面氢的脱附速率的活化能一致。这一结果表明，硅的生长受到氢的解吸的限制。研究发现，单独添加过量的氢原子增加了硅表面氢的覆盖率，降低了硅膜的生长速率，这表明氢可以控制硅膜的生长。此外，还澄清了吸附的氢原子阻碍了硅原子和硅氢化物等前驱体的表面迁移。2)在Ge2.5ML/Si（100）衬底上生长Si时，观察到Ge原子的表面偏析。从锗偏析的衰变长度来看，过量的氢是阻碍锗偏析的有效因素。然而，多余的氢原子加速了孤岛生长。这些事实表明，氢原子严重影响了硅的生长机制。

We have investigated growth processes of thin films, such as epitaxy and oxidation, by high-resolution electron energy loss spectroscopy and reflection high-energy electron diffraction. Especially, hydrogen has been focused on our attention because it plays an important role of the growth processes. Therefore, we have studied influences of hydrogen on Ge/Si epitaxial growth using Si_2H_6 and obtained the main results as follows :1) In the case of Si growth on Si(100) surfaces at temperatures below 550ﾟC、the activation energy of growth rate is in agreement with that of desorption of hydrogen from Si(100) surfaces. This result indicates that the Si growth is limited by the desorption of hydrogen. It has been found that excess hydrogen atoms added separately increase the hydrogen coverage on the Si surface and lower the growth rate, which suggests the possibility of a control of film growth using hydrogen. Moreover, it has been clarified that the adsorbed hydrogen atoms hinder the surface migration of precursors such as Si atoms and Si hydride species.2) In the case of Si growth on Ge2.5ML/Si(100) substrates, the surface segregation of Ge atoms is observed. From the evaluation of the decay length for Ge segregation, excess hydrogen is effective for hindering the segregation. However, the excess hydrogen atoms accelerate the islanding growth. These facts indicate that hydrogen atoms seriously influence the mechanism of Si growth.