Study on the formation of CoSi_2/Si(100) heterostructures by reactive epitaxial growth

由于CoSi_2薄膜可以在Si（100）表面外延生长，因此有望作为ULSI器件的外延接触层。在本计画中，我们利用扫描穿隧显微镜与穿透电子显微镜，阐明了在Si（100）表面上形成厚度为20 nm的外延CoSi_2薄膜的自对准硅化物技术，以及控制Co/Si界面反应的物理因素。此外，我们还发展了两步生长法，并研究了第一步超薄CoSi_2（100）外延膜的形成机理。为了提高超薄CoSi_2（100）薄膜的覆盖率和平整度，在CoSi_2（100）/Si（100）外延生长中引入了O、Sb、Ge和Al等附加元素作为中间层，并阐明了附加元素对外延生长机制的影响。（1）CoSi_2（100）薄膜的外延生长 关于我们 n Si（100）表面，以类似于Stranski-Krastanov生长模式的生长方式。Si（100）表面的缺陷和台阶作为CoSi_2（100）薄膜的成核点，促进了多层成核和层生长，提高了薄膜的覆盖率。（2）在两步外延生长中，没有观察到具有{115}面的三维CoSi_2岛，并且CoSi_2（100）表面上的针孔和沟道的深度远小于反应沉积外延。认为CoSi_2（100）薄膜表面覆盖Si原子的台阶结构起着形核位置的作用。结果，在Co沉积期间进行具有多个成核和层生长的外延生长。此外，第一步超薄CoSi_2（100）膜促进了层的生长，抑制了针孔周围Si原子从衬底的扩散，从而实现了平整的表面。（3）在O和Al原子用作中间层的情况下，膜覆盖率和平坦度显著改善。特别是在470℃的氧原子固相外延中，可以获得无针孔、原子级平整的CoSi_2（100）薄膜。在3 ML厚的Al层间膜的情况下，形成在其置换位置中随机具有Si原子的CoAl膜。在Sb和Ge中间层的情况下，观察到了具有孪晶结构的CoSi_2岛。少

CoSi_2 is expected as an epitaxial contact in ULSI devices since the CoSi_2 film can be epitaxially grown on a Si(100) surface. In this project, in order to realize a salicide technique, by which a 20-nm-thick epitaxial CoSi_2 film required for Si-ULSI processes can be formed on a Si(100) surface, we have clarified the solid-phase reaction at Co/Si interfaces and its physical factors dominating the reactions, using scanning tunneling microscopy and transmission electron microscopy. In addition, we have developed a two-step growth method and investigated the formation mechanisms of the first-step ultra-thin CoSi_2(100) epitaxial film. For improving the coverage and the flatness of the ultra-thin CoSi_2(100) film, additional elements such as O, Sb, Ge and Al have been introduced as an intermediate layer in the CoSi_2(100)/Si(100) epitaxial growth and we have clarified the effects of the additional elements on the epitaxial growth mechanisms.( 1 ) CoSi_2(100) films are epitaxially grown o … More n Si(100) surfaces in a similar growth manner of a Stranski-Krastanov growth mode. Defects and steps on the Si(100) surface act as nucleation sites of a CoSi_2(100) film, and multiple nucleation and layer growth is enhanced, resulting in the improvement of the film coverage.( 2 ) In the two-step growth, no 3-dimensional CoSi_2 island with {115} facets is observed, and the depth of pinholes and channels on the CoSi_2(100) surface is much less than that in reactive deposition epitaxy. It is considered that the step structures on the CoSi_2(100) film surface covered with Si atoms play a role of a nucleation site. As a result, epitaxial growth with multiple nucleation and layer growth proceeds during Co deposition. In addition, the first-step ultra-thin CoSi_2(100) film enhances the layer growth and suppresses the diffusion of Si atoms from the substrate around the pinhole, which leads to the realization ofa flat surface.( 3 ) In the case of O and Al atoms used as an intermediate layer, the film coverage and flatness are significantly improved. Especially, in the 470℃ solid-phase epitaxy with O atoms, a pinhole-free and atomically-flat CoSi_2(100) film can be realized. In the case of 3-ML-thick Al interlayer film, a CoAl film randomly with Si atoms in its substitutional positions is formed. On the other hand, in the cases of a Sb and Ge interlayer, CoSi_2 islands with a twin structure are observed. Less