Composition optimization of HfxZr1-xO2 thin films to achieve the morphotrophic phase boundary for high-k dielectrics

HfxZr1-xO2 thin films exhibit a high dielectric constant at the morphotropic phase boundary (MPB), which is beneficial for high-k dielectric applications. To minimize the equivalent oxide thickness, the effects of various HZO thicknesses and compositions on the MPB were investigated. In general, HZO films with a thickness of 10 nm exhibit a high dielectric constant owing to MPB at a composition of Hf:Zr = 3:7. However, it was confirmed that composition optimization is required for HZO films with thicknesses below 10 nm to achieve an MPB. As the HZO thickness decreases, a low Zr ratio is favorable for achieving a high dielectric constant (>45) by MPB, which is expected to be due to the large impact of the interface that consequently induces a change in phase formation. Results of electrical and x-ray diffraction analyses confirmed that a high dielectric constant was obtained when the ratio of the tetragonal phase increased and that the tetragonal phase was well formed at a low Zr ratio in the 6 nm-thick HZO film. Therefore, the optimal ratio between the tetragonal and orthorhombic phases should be determined to achieve MPB in HZO thin films, and this can be achieved by composition optimization.