Method to Achieve the Morphotropic Phase Boundary in HfxZr1-xO2 by Electric Field Cycling for DRAM Cell Capacitor Applications

We demonstrate a novel method using electric field cycling to induce a phase transition in HfxZr1−xO2 to reach the morphotropic phase boundary of tetragonal and orthorhombic phase. Conventional methods used to induce the phase transition, such as high temperature annealing, cannot be used with the DRAM cell capacitor fabrication process because it associates with grain enlargement, increased leakage current, and a narrow process margin due to the metastability of the morphotropic phase boundary. To achieve an morphotropic phase boundary in HfxZr1−xO2 without high temperature annealing and without increasing leakage current, we propose a two-step process, using low temperature annealing to form the tetragonal phase and electric field cycling to achieve the morphotropic phase boundary of tetragonal and orthorhombic phase in HfxZr1−xO2 film. This approach enabled us to achieve both low voltage with high dielectric k value, and low leakage current, meeting the requirements for the next-generation DRAM cell capacitor dielectric materials.