Abstract
A comparison study on electrical performance of Ge pMOSFETs with a GeOx passivation layer formed by ozone post oxidation (OPO) and plasma post oxidation (PPO) is performed. PPO and OPO were carried out on an Al2O3/n-Ge (001) substrate followed by a 5-nm HfO2 gate dielectric in situ deposited in an ALD chamber. The quality of the dielectric/Ge interface layer was characterized by X-ray photoelectron spectroscopy and transmission electron microscopy. The PPO treatment leads to a positive threshold voltage (VTH) shift and a lower ION/IOFF ratio, implying a poor interface quality. Ge pMOSFETs with OPO exhibit a higher ION/IOFF ratio (up to four orders of magnitude), improved subthreshold swing, and enhanced carrier mobility characteristics as compared with PPO devices. A thicker Al2O3 block layer in the OPO process leads to a higher mobility in Ge transistors. By comparing two different oxidation methods, the results show that the OPO is an effective way to increase the interface layer quality which is contributing to the improved effective mobility of Ge pMOSFETs.
Highlights
With conventional complementary metal-oxide-semiconductor (CMOS) devices approaching its physical limit, performance enhancement is hard to realize for highspeed semiconductor devices with silicon (Si) as the channel material
We demonstrate that ozone post oxidation (OPO) is a promising passivation technique for future Ge Metal-oxide-semiconductor field-effect transistors (MOSFETs) fabrication
Ge pMOSFETs are realized with Germanium oxide (GeOx) passivation, which is formed by OPO or plasma post oxidation (PPO) treatment of Aluminum oxide (Al2O3)/ n-Ge in PEALD
Summary
With conventional complementary metal-oxide-semiconductor (CMOS) devices approaching its physical limit, performance enhancement is hard to realize for highspeed semiconductor devices with silicon (Si) as the channel material. Replacing substrate or channel material with other material with high mobility is an imperative option. Germanium (Ge) has been considered as a promising alternative channel material owing to higher carrier mobility than that of Si. The MOSFET usually needs a high-quality oxide/semiconductor interface to reach high effective mobility. For quite a long history, Ge MOSFETs suffered from the high interface state density (Dit) caused by the poor thermal stability of GeO2 and dangling bonds [1]. Plenty of research has been carried out on Ge interface passivation
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