Lowering Dielectric Constant of Ferroelectric HZO Film with Ultra-Thin Al2O3 Intermediate Layer

Abstract

HfO2-based ferroelectric thin films have been one of the most active research topics in the semiconductor device field recently. However, the metal-ferroelectric-insulator-semiconductor (MFIS) structure used as a gate stack has an inevitable limitation of significant voltage drop across the insulator layer. It comes from the fairly large difference in dielectric constant between ferroelectric and insulator layers. In this study, we suggest that the dielectric constant of Hf0.5Zr0.5O2 (HZO) ferroelectric film can be reduced sufficiently while maintaining its ferroelectricity. An ultra-thin Al2O3 layer inside the HZO film is inserted to make HZO/Al2O3/HZO trilayer structure during atomic layer deposition process. In conjunction with TiN electrodes deposited in the Ar-rich environment during the magnetron sputtering process, the trilayer structure is found to have an effective dielectric constant of ~18 without deteriorating its ferroelectricity. This effective dielectric constant is ~37% smaller than the dielectric constant of normal ferroelectric HZO single layer and is even smaller than the value calculated theoretically by considering the series connection of the trilayer. Our work can provide a practical guide for reducing the switching voltage and increasing the stability of ferroelectric polarization in the devices adopting the MFIS structure.