Making Metallic Thin Films Atomically Flat

Can we control the flatness of the surface of a thin film down to the level of individual atoms? Can we further make such an ultraflat surface on a wafer scale? For such purposes, the current deposition methods, including molecular beam epitaxy (MBE), atomic layer deposition (ALD) and conventional sputtering methods, are still not adequate. In this article, we introduce a novel thin film deposition technique developed by modifying a simple sputtering method to make atomically flat metallic surfaces and a new way to investigate the structural details of thin films grown at the atomic level. For thin film, heteroepitaxial growth of a crystalline film on a different crystalline substrate is usual, and the lattice mismatch between the crystalline film and the substrate occurring in heteroepitaxy produces many misfits at the interface, which create various defects, including dislocations and grain boundaries that eventually lead to a rough surface and the deterioration of the overall quality of the crystal. The metamorphic growth method utilizing the extended atomic distance mismatch (EADM) helps to achieve successful growth of thin films in spite of a large lattice mismatch by calculating the match for a relatively long period in advance. Having an ultraflat surface for thin films made of metals such as copper has many advantages. Several advantages and possible applications of metal thin films with ultraflat surfaces are introduced.