Effect of Yttrium Feeding Time on the Electrical and Structural Properties of Atomic Layer Deposited Y-doped TiO2 Films for Dynamic Random-Access Memory Capacitor

Abstract

This study systematically investigates the impact of yttrium (Y) and aluminum (Al) dopant concentrations and their distributions in rutile-structured TiO₂ films grown via atomic layer deposition (ALD) for dynamic random-access memory capacitors. Excessive amounts of the Y and Al dopants in the doping layer can induce localized Y₂O₃ and Al₂O₃ regions, which disrupt the crystallization of the TiO₂ layer into the high-k rutile phase. To address this issue, a subtle modulation of dopant concentrations is attempted by controlling the dopant feeding time in a single unit ALD cycle. This sub-one-cycle doping effectively prevents the localization of dopants, particularly for the Y dopant, enabling substitutional Y incorporation to efficiently decrease leakage current while minimizing a decrease in the dielectric constant of the TiO₂ layer. An optimized yttrium-doped TiO₂ capacitor was fabricated with controlled dopant concentration and distribution, achieving a minimum equivalent oxide thickness of 0.50 nm and a physical oxide thickness of 8.4 nm while maintaining a leakage current density below 10⁻⁷ A/cm².