In-situ post-doping plasma process during atomic layer deposition of Al-doped TiO2 for sub-nanometer lattice ordering and defect annihilation

Abstract

Atomic layer deposition (ALD) is extensively used to fabricate doped dielectrics due to its ability to deposit conformal films with atomic-scale thickness control. Al-doped TiO2 (ATO) is a promising high-k dielectric for dynamic random access memory (DRAM) applications, offering a high dielectric constant with a remarkable leakage-lowering effect by Al acceptor doping. However, ATO fabrication via conventional supercycle-based ALD suffers from severe crystallinity loss during the growth of TiO2 upon Al doping owing to the dopant-induced lattice disorder. In addition, Al doping cannot reduce any inherent O vacancies (VO) of TiO2, although the original purpose of doping was to address the n-type nature caused by VO. To resolve these limitations, we propose a single-step, in-situ Ar/O2 post-doping plasma (PDP) process immediately after the Al dopant incorporation. Using the PDP process, simultaneous atomic-scale dopant migration-mediated crystallization and VO annihilation were successfully initiated. Thus, the surface concentration of the dopant decreased, reducing the dopant-induced lattice distortion, while promoting the highly crystallized seed layer-like surface. Consequently, strong rutile-phase recovery was accompanied by enhanced lattice-matched growth. In addition, the PDP process significantly lowers the VO-to-lattice oxygen ratio by facilitating the recombination between reactive O species and VO, increasing the corresponding 0.4 eV of conduction band offset (CBO). Despite the common trade-off between the dielectric constant and leakage, the Pt/PDP-ATO/Ru capacitor exhibited a simultaneous 30% increase in dielectric constant and up to a 1.6-order reduction in leakage current density.