A Ferroelectric Property Tailoring Method of Al0.7Sc0.3n Films by Sputter-Deposition Pressure

Abstract

New ferroelectric materials have been extensively studied for scaled non-volatile memory [1]. Among materials, Al1-x Sc x N (ASN) films are attracting attention owing to their high remnant polarization (Pr ) of over 100 µC/cm2 [2]. Although the material is started to be characterized, a high coercive field (E c) with a relatively high leakage current has been an issue. As reactive sputtering used to deposit nitrides is known to be influenced by the condition, in this study, we have changed the sputtering pressure for ASN deposition and characterized the ferroelectric properties. The composition of the ASN films is Al0.7Sc0.3N.Metal-insulator-metal (MIM) capacitors with 50-nm-thick ASN film capacitors with TiN electrodes were fabricated by a reactive sputtering process. We varied the sputtering pressure from 0.76 to 1.1 Pa. Figure 1 shows the leakage current (J-V) of the capacitors. The capacitor with a low-pressure ASN film shows a relatively low leakage current and a breakdown field (E BD) of 8 MV/cm which is high considering the bandgap of the ASN film to be 3.2 eV. On the other hand, the capacitor with a high-pressure ASN film showed a high leakage current with a reduced E BD of 5.2 MV/cm. As the leakage current is determined by the interface, stacking the ASN layers may result in reducing the leakage current while maintaining a high E BD. The leakage current of a capacitor with a 5-nm-thick low-pressure ASN at each interface and a 40-nm-thick high-pressure ASN film is also shown in fig. 1. We see a slight suppression in the leakage current and improvement in the E BD to be 6.2 MV/cm. P r of the capacitors were obtained by positive-up-negative-down (PUND) measurements. The pulse-height dependent P r is shown in fig. 2. The capacitor with a low-pressure ASN film revealed a high E c of 3.8 MV/cm, while the one with a high-pressure ASN film was 3.4 MV/cm. The capacitor with stacked ASN films showed the same E c of 3.4 MV/cm. The capacitors with single film showed a gradual change in the P r on the electric field. In the stacked one, in contrast, a sharp change in the electric field with a constant P r of 100 μC/cm2 was obtained.In conclusion, stacked ASN films deposited by different sputter pressures show reduced leakage current with a high breakdown field. Although the physical change by the pressure is still unknown, tailoring the interface and bulk regions has a possibility to further improve the ferroelectric properties.