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

Abstract

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.

Slow Trap Properties and Generation in Al2O3/GeOx/Ge MOS Interfaces Formed by Plasma Oxidation Process

“…22 This result suggests that the location of slow traps is close to the GeO x /Ge interfaces for n-Ge MOS interfaces, as concluded for the post-PO Al 2 O 3 /GeO x /n-Ge MOS structures. 22 On the other hand, it is found in Figure 4d that the Al 2 O 3 /GeO x /p-Ge gate stacks with a significant GeO x thickness leads to a lower ΔN st and that thinner GeO x leads to higher ΔN st at a given E ox . This result means that the areal slow trap density decreases with an increase in the GeO x thickness, which can be interpreted by considering that the main slow traps for holes exist close to the Al 2 O 3 /GeO x interfaces.…”

“…We have also reported the slow trap behavior of ALD Al 2 O 3 /GeO x /n-Ge MOS interfaces formed by post-PO and n-channel MOSFETs using these MOS interfaces. 22 Effective slow trap density at the Ge MOS interfaces and the time constant of the source current in Ge n-MOSFETs do not significantly change with varying the thickness of Al 2 O 3 and GeO x , which has been demonstrated. These results have indicated that the main slow traps for electrons exist inside the GeO x /Ge control layers.…”

“…Any defects in the insulators in MOS interfaces including Al 2 O 3 − and Ge oxides , could be these slow trap physical origins, which have recently been reported. We have also reported the slow trap behavior of ALD Al 2 O 3 /GeO x /n-Ge MOS interfaces formed by post-PO and n-channel MOSFETs using these MOS interfaces .…”

“…Any defects in the insulators in MOS interfaces including Al 2 O 3 − and Ge oxides , could be these slow trap physical origins, which have recently been reported. We have also reported the slow trap behavior of ALD Al 2 O 3 /GeO x /n-Ge MOS interfaces formed by post-PO and n-channel MOSFETs using these MOS interfaces . Effective slow trap density at the Ge MOS interfaces and the time constant of the source current in Ge n-MOSFETs do not significantly change with varying the thickness of Al 2 O 3 and GeO x , which has been demonstrated.…”

“…13−16 Nevertheless, the poor bias-temperature instability (BTI) characteristics caused by a large amount of slow traps existing in MOS structures is also a serious remaining issue for these Ge gate stacks. 17−19 Any defects in the insulators in MOS interfaces including Al 2 O 3 18−21 and Ge oxides 22,23 could be these slow trap physical origins, which have recently been reported. We have also reported the slow trap behavior of ALD Al 2 O 3 /GeO x /n-Ge MOS interfaces formed by post-PO and n-channel MOSFETs using these MOS interfaces.…”