Electrode-dependent interfacial reactions and Ru loss suppression during ozone-based atomic layer deposition of TiO2 on Ru- and RuO2-based electrodes

초록

This study investigates electrode-dependent interfacial reactions occurring 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 reactions 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. 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.

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