Surface and Interface Smoothing of Epitaxial CoSi₂ Films by Solid-Phase Epitaxy Using Adsorbed Oxygen Layers and Two-Step Growth on Si(001) Surfaces

The oxygen-mediated two-step growth of high-quality CoSi₂(001) films on Si(001) is demonstrated. In the first-step growth, uniform 6-monolayers (ML)-thick CoSi₂(001) films with atomically flat surfaces and interfaces are grown by solid-phase epitaxy (SPE) at 470°C of 3 ML Co on O-adsorbed Si and O-covered 3 ML Co on clean Si. In both cases, O atoms improve the surface and interface flatness in SPE growth. In the second-step growth, 5.6 nm Co is solely deposited at 470°C on the O-covered CoSi₂ template. We successfully achieve the growth of 20-nm-thick CoSi₂(001) films with smooth surfaces and abrupt interfaces. In the O-mediated two-step growth, O atoms segregating to the film growth front suppress the lateral migration of Co atoms. Furthermore, in the second-step growth, the uniform template promotes homogeneous growth and keeps the surfaces and interfaces of CoSi₂ films smooth. This novel technique, applicable to salicide processes, is highly suitable for the formation of epitaxial CoSi₂ contacts in future ULSI devices.