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. © 2024 Elsevier B.V.