Reduction of Slow Trap Density in Al2O3/GeOxNy/n-Ge MOS Interfaces by PPN-PPO Process

The realization of high-k/IL/Ge MOS interfaces with thin equivalent oxide thickness (EOT), low interface state density (Dit), 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 (Nst) and Dit in Al
₂
O
₃
/GeO
_x
N
_y
/n-Ge MOS interfaces formed by atomic layer deposition (ALD) Al
₂
O
₃
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 Al
₂
O
₃
/GeO
_x
N
_y
/nGe MOS interface properties. It is found that N atoms induced into GeOx can suppress slow electron trapping. An Al
₂
O
₃
/n-Ge structure with 1-min PPN before PPO can reduce Nst by 34% in a weak electric field, whereas PPN after PPO increase Nst. Also, the sufficient time PPO process after PPN can decrease Dit to a similar level as that at the Al
₂
O
₃
/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.