Heterogeneous Local-Epitaxial Growth Behavior of Ultrathin HfO2/Al-Doped TiO2 Bilayer Dielectrics for Dynamic Random-Access Memory Capacitor Applications

초록

This study systematically examines the growth behavior and interfacial properties of a HfO2/Al-doped TiO2 (ATO) bilayer deposited on a Ru thin-film bottom electrode. Local-epitaxial growth of ATO into the rutile structure proceeds in two distinct, thickness-dependent stages that ultimately influence the crystallinity and interfacial integrity of the subsequently grown HfO2 capping layer. At low ATO thicknesses (<4-4.5 nm), a coherent interface with strained rutile ATO is stabilized by the dominant influence of the underlying in situ-formed RuO2. Conversely, at higher ATO thicknesses (>4-4.5 nm), an incoherent interface with relaxed rutile ATO becomes energetically preferred due to the increased volumetric energy contribution of the ATO. On coherently grown rutile ATO, the HfO2 capping layer stabilizes in the higher-k tetragonal phase by efficient local lattice matching between aligned tetragonal HfO2 and rutile ATO planes. In contrast, incoherent rutile ATO promotes disorder/intermixing, and monoclinic HfO2 can emerge as the HfO2 thickness increases. An appropriate r-ATO thickness region preserves insulating integrity and minimizes interfacial low-k layer effects. A Pt/HfO2/ATO/Ru capacitor achieves a minimum equivalent oxide thickness of 0.62 nm at a minimum physical thickness of 5.9 nm, while maintaining sufficiently low leakage current level (<10(-7) A/cm(2) at 0.8 V).

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