Reduction of Slow Trap Density in Al2O3/GeO x N y /n-Ge MOS Interfaces by PPN-PPO Process

Abstract

The realization of high- ${k}$ /IL/Ge MOS interfaces with thin equivalent oxide thickness (EOT), low interface state density ( $\text{D}_{{\text {it}}}$ ), and high reliability is strongly needed for realizing Ge metal–oxide–semiconductor field-effect transistors (MOSFETs). In this article, we examine the properties of the slow trap areal density ( $\Delta \text{N}_{{\text {st}}}$ ) and $\text{D}_{{\text {it}}}$ in Al2O3/GeOxN y /n-Ge MOS interfaces formed by atomic layer deposition (ALD) Al2O3 films with plasma post nitridation (PPN) and plasma post oxidation (PPO). Here, the process order and process time of PPN and PPO are systematically changed to optimize the Al2O3/GeO x N y /n-Ge MOS interface properties. It is found that N atoms induced into GeO x can suppress slow electron trapping. An Al2O3/n-Ge structure with 1-min PPN before PPO can reduce $\Delta \text{N}_{{\text {st}}}$ by 34% in a weak electric field, whereas PPN after PPO increase $\Delta \text{N}_{{\text {st}}}$ . Also, the sufficient time PPO process after PPN can decrease $\text{D}_{{\text {it}}}$ to a similar level as that at the Al2O3/GeO x /n-Ge MOS interfaces. The temperature dependence of electron trapping properties is also experimentally evaluated. The slow electron trapping is expected to be more suppressed for the GeO x N y interfaces at real device operation temperature.