Rutile Without Substrate Limitations: Top-Interface-Driven Crystallization of TiO₂

Controlling the polymorphic phases within the thermal budget of atomic layer deposition (ALD) is essential for integrating high-k dielectrics into dynamic random-access memory (DRAM) capacitors. Rutile TiO₂ offers a dielectric constant significantly higher than that of tetragonal ZrO₂ and anatase TiO₂. However, its application on industry-standard TiN electrodes is impeded by the lack of rutile-compatible lattice matching. A top-interface-driven stabilization strategy is demonstrated, where a structurally compatible RuO₂ upper layer stabilizes rutile TiO₂ at 400°C regardless of the crystallinity of the underlying ZrO₂/TiN stack. Thickness-dependent phase maps reveal an interfacial-energy-driven anatase-to-rutile transition for thin amorphous TiO₂ layers, enabling rutile formation even on amorphous ZrO₂. The resulting TiO₂/ZrO₂/TiN capacitors exhibit a dielectric constant of approximately 80 and a reduced equivalent oxide thickness, comparable to that of ZrO₂-based stacks. A methanol-assisted reduction-etching process allows selective removal of RuO₂ by O₃ with minimal TiN oxidation. This top-interface engineering concept offers a substrate-agnostic approach to rutile TiO₂ that is compatible with DRAM process windows and can be extended to other polymorphic oxides.