Mengnan Ke

Properties of slow traps of ALD Al2O3/GeOx/Ge nMOSFETs with plasma post oxidation

The realization of Ge gate stacks with a small amount of slow trap density as well as thin equivalent oxide thickness and low interface state density (Dit) is a crucial issue for Ge CMOS. In this study, we examine the properties of slow traps, particularly the location of slow traps, of Al2O3/GeOx/n-Ge and HfO2/Al2O3/GeOx/n-Ge MOS interfaces with changing the process and structural parameters, formed by atomic layer deposition (ALD) of Al2O3 and HfO2/Al2O3 combined with plasma post oxidation. It is found that the slow traps can locate in the GeOx interfacial layer, not in the ALD Al2O3 layer. Furthermore, we study the time dependence of channel currents in the Ge n-MOSFETs with 5-nm-thick Al2O3/GeOx/Ge gate stacks, with changing the thickness of GeOx, in order to further clarify the position of slow traps. The time dependence of the current drift and the effective time constant of slow traps do not change among the MOSFETs with the different thickness GeOx, demonstrating that the slow traps mainly exist near the interfaces between Ge and GeOx.

Understanding of slow traps generation in plasma oxidation GeO x /Ge MOS interfaces with ALD high-k layers

A small amount of slow trap density in Ge gate stacks is a crucial issue for Ge CMOS, in addition to thin equivalent oxide thickness and low interface state density. In this paper, we study the slow trap position and the generation mechanism in the high-k/GeO<inf>x</inf>/Ge interfaces fabricated by plasma oxidation. The slow trap density in Al<inf>2</inf>O<inf>3</inf>/GeO<inf>x</inf>/Ge interfaces by plasma pre-oxidation is compared with different GeO<inf>x</inf> and Al<inf>2</inf>O<inf>3</inf> thickness, and the interfaces by plasma post oxidation (PPO). ALD Al<inf>2</inf>O<inf>3</inf>, HfO<inf>2</inf>, La<inf>2</inf>O<inf>3</inf> and Y<inf>2</inf>yO<inf>3</inf>/GeO<inf>x</inf>/Ge MOS interfaces are compare in terms of the slow trap density. It is found the main slow traps in Al<inf>2</inf>O<inf>3</inf>/GeO<inf>x</inf>/Ge can locate near the GeO<inf>x</inf>/Ge interfaces for electrons and the Al<inf>2</inf>O<inf>3</inf>/GeO<inf>x</inf> interface for holes. It is also found that additional slow traps near conduction band side are generated during the PPO process. It is revealed that slow traps are generated by post high-k ALD, while Al<inf>2</inf>O<inf>3</inf> provides the lowest slow trap density in comparison with Y<inf>2</inf>O<inf>3</inf>, HfO<inf>2</inf> and La<inf>2</inf>O<inf>3</inf> high-k films.