Electrode-Dependent Interfacial Reactions and Ru Loss Suppression during Ozone-Based Atomic Layer Deposition of TiO2 on Ru- and RuO2-Based Electrodes

Abstract

This study investigates electrode-dependent interfacial reactions during ozone-based atomic layer deposition (ALD) of rutile TiO₂ thin films on Ru- and RuO₂-based bottom electrodes for dynamic random-access memory (DRAM) capacitors. By comparing Ru, RuO₂, RuO₂/TiN, and RuO₂/Ru bottom electrodes, the mechanisms governing Ru loss, Ru-loss suppression, and initial TiO₂ overgrowth were clarified. The Ru-loss-free behavior of RuO₂/Ru suggested the oxygen supply from the buried RuO₂/Ru interface, which can support Ti precursor reaction while suppressing direct reduction of the top RuO₂ surface. Among these platforms, Ru and RuO₂/Ru were further examined to determine how their distinct interfacial reactions govern TiO₂ growth, crystallization, morphology, and electrical properties. RuO₂/Ru provided strong rutile templating and high dielectric constants, but excessive initial overgrowth caused morphological nonuniformity and leakage degradation. RuO₂/Ru provided strong rutile templating and high dielectric constants, but excessive initial overgrowth caused morphological nonuniformity and leakage degradation. Metallic Ru showed a lower leakage current but required suppression of ozone-induced Ru loss to improve its dielectric performance. A sequential ALD process combining repeated precursor feeding with controlled initial ozone exposure was therefore developed for Ru bottom electrodes. This process suppressed Ru loss while preserving rutile TiO₂ crystallization, minimizing the interfacial low-capacitance layer and improving dielectric scaling. As a field-relevant metal-insulator-metal capacitor demonstration of this process improvement, Al-doped TiO₂ deposited using this process achieved an equivalent oxide thickness of 0.43 nm at a physical oxide thickness of 8.5 nm while satisfying the DRAM leakage-current criterion.