Na doping process using UV and NaOH solution for leakage current reduction in TiO2 dielectric films

Abstract

In this study, we demonstrate a simple post-process to dope Na ions into pre-fabricated TiO₂ dielectric thin films using UV irradiation with a NaOH aqueous solution and analyze the distribution of the doped Na dopants within the thin film as well as their effect on the electrical properties. The TiO₂ thin films deposited on the bottom electrode by atomic layer deposition (ALD) were immersed in a 30 wt% NaOH aqueous solution and irradiated with UV light for 5 min to induce the desolvation of Na⁺ and OH⁻ ions in the solution, thereby facilitating Na⁺ and OH^– ion doping within the TiO₂ thin film. Secondary ion mass spectrometry analysis confirmed that Na⁺ ions activated by UV exposure penetrated the TiO₂ film up to 1.5 nm (bulk diffusion), 5 nm (dislocation diffusion), and 15 nm (grain boundary diffusion) from the surface. Only the TiO₂ films irradiated by UV in the NaOH solution showed a significant reduction in leakage current. Consequently, we successfully achieved doping through a simple method by activating solvated ions in a NaOH solution under UV irradiation, which could improve the leakage characteristics of the oxide thin film caused by intrinsic (or extrinsic) defects.