Effect of Al doping on structural and electrical properties of HfO2/ZrO2 layered structures for high-k applications

Abstract

ZrO₂ films with ultrathin Al₂O₃ layers have effectively contributed to the miniaturization of dynamic random access memory (DRAM) capacitors for many years. However, as memory devices continue to shrink, higher dielectric constants are required to maintain cell capacitance. To address this challenge, research has explored the use of tetragonal HfO₂ layers, which theoretically possess a higher dielectric constant than ZrO₂, as dielectrics. However, the thermodynamically stable phase of HfO₂ is monoclinic with a lower dielectric constant, necessitating a phase transition to the tetragonal form for DRAM capacitor applications. Although attempts have been made to induce this phase transition to achieve high dielectric constants by applying an HfO₂/ZrO₂ layered structure or doping HfO₂ with elements such as Zr, Al, and Si, significant challenges remain in completely eliminating the monoclinic phase or implementing a pure tetragonal phase of HfO₂. In this study, we systematically investigated the crystallinity changes and improved the electrical properties of HfO₂/ZrO₂ layered structures with Al doping in the HfO₂ layers. Our findings demonstrate that optimizing the partitioning of the ZrO₂ and HfO₂ layers, combined with Al doping, effectively achieves equivalent oxide thickness scaling.