WS2 Film by Sputtering and Sulfur-Vapor Annealing, and its pMISFET With TiN/HfO2 Top-Gate Stack, TiN Bottom Contact, and Ultra-Thin Body and Box

Takuya Hamada,Kuniyuki Kakushima,Taiga Horiguchi,Iriya Muneta,Satoshi Igarashi,Hitoshi Wakabayashi,Shigetaka Tomiya,Tetsuya Tatsumi,Masaya Hamada,Kazuo Tsutsui

doi:10.1109/jeds.2021.3108882

Takuya Hamada, Kuniyuki Kakushima + Show 8 more

Open Access

https://doi.org/10.1109/jeds.2021.3108882

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Abstract

A layered polycrystalline WS2 film is formed by radio-frequency (RF) magnetron sputtering and sulfur-vapor annealing (SVA). Its pMISFET is successfully demonstrated with TiN/HfO2 top-gate stack, TiN contact, and ultra-thin body and box technologies. A WS2 film with a (002) plane is formed parallel to a substrate surface using RF magnetron sputtering, and its crystallinity is drastically enhanced by the SVA. I–V characteristics with p-type operation are confirmed in WS2 MISFETs with a maximum field effect mobility of 1.5 × 10-2 cmV-1s-1. Therefore, our film-formation method is a promising candidate for pMOSFETs in CMOS circuits.

Highlights

S ILICON technology with FinFETs in logic LSIs has been scaled down to the 5-nm technology node [1], [2]
From a cross-sectional transmission electron microscopy (TEM) image of the WS2 film formed by sputtering and sulfur-vapor annealing (SVA) shown in Fig. 1, a layered structure parallel to the SiO2 surface is confirmed
An out-of-plane Xray diffraction (XRD) pattern is shown in Fig. 2. (002) plane peaks in WS2 films with and without SVA are observed, which indicate that layered WS2 film was formed during the sputtering process

Summary

Introduction

S ILICON technology with FinFETs in logic LSIs has been scaled down to the 5-nm technology node [1], [2]. Nano-sheet and fork-sheet devices have been recently proposed beyond 5 nm, they need thin channels in several-nanometer size, in which a scattering is required to be controlled to enhance a mobility [3]. With respect to the silicon (Si), it has been reported that the mobility decreases with a decrease in the channel thickness due to an increase in the scattering effect by the dangling bonds at Si surface. A tungsten disulfide (WS2) film among a transition metal di-chalcogenide (TMDC) has an atomically thin 2D structure without dangling bond, resulting in high mobility. A calculated high mobility has been reported to be more than 1,000 cm2V−1s−1 for a mono layer [4]. WS2 films as well as films of other TMDCs are expected to be applicable to advanced LSIs and to energy harvesters, displays and sensors [5]–[11]

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