Impact of interlayer insulator formation methods on HfOx ferroelectricity in the metal-ferroelectric-insulator-semiconductor stack

Abstract

It has been reported that the HfOx-based metal-ferroelectric-insulator-semiconductor (MFIS) stack is one of the most feasible structures for memory applications in ferroelectric devices. In addition, in MFIS stacks, the formation of a high-quality thin insulator is considered to be a crucial process, because it determines the device performance and reliability. In this study, the effects of different SiO2 thin interfacial layers (ILs) formed by chemical oxidation and atomic layer deposition (ALD) on the ferroelectricity of HfOx were investigated in MFIS stacks. Notably, the IL formation method affected the crystallization temperature of HfOx ferroelectricity. In particular, the chemical oxide IL sample was sufficiently crystallized only at an RTA temperature greater than 800 & DEG;C, whereas the ALD oxide IL sample began to undergo a complete ferroelectric phase transition from a low temperature (600 & DEG;C). The x-ray analysis verified that the IL formation method affected the initial film state of the HfOx layer by modulating the Hf-O bonding states, resulting in a different temperature dependence for ferroelectricity formation during the subsequent crystallization annealing stage. Consequently, it was confirmed that stable polarization (2P(r) > 30 mu C/cm(2)) could be obtained over a wide temperature range (600-800 & DEG;C) through IL material engineering; this could facilitate the integration of HfOx-based ferroelectric devices in terms of the heat budget and the application of ferroelectric devices as commercial devices.