| Co-Investigator(Kenkyū-buntansha) |
IKEDA Hiroya Nagoya University, Graduate School of Engineering, Assistant Professor, 工学研究科, 助手 (00262882)
YASUDA Yukio Nagoya University, Graduate School of Engineering, Professor, 工学研究科, 教授 (60126951)
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| Research Abstract |
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
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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
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