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

Abstract

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.