Gas-Source CVD Growth of Atomic Layered WS2 from WF6 and H2S Precursors with High Grain Size Uniformity

Mitsuhiro Okada,Tetsuo Shimizu,Wen-Hsin Chang,Yasumitsu Miyata,Atsushi Ando,Naoya Okada,Toshitaka Kubo,Toshifumi Irisawa,Takahiko Endo

doi:10.1038/s41598-019-54049-6

Mitsuhiro Okada, Tetsuo Shimizu + Show 7 more

Open Access

https://doi.org/10.1038/s41598-019-54049-6

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Abstract

Two-dimensional (2D) transition-metal dichalcogenides have attracted a considerable amount of attention because of their potential for post-silicon device applications, as well as for exploring fundamental physics in an ideal 2D system. We tested the chemical vapour deposition (CVD) of WS2 using the gaseous precursors WF6 and H2S, augmented by the Na-assistance method. When Na was present during growth, the process created triangle-shaped WS2 crystals that were 10 μm in size and exhibited semiconducting characteristics. By contrast, the Na-free growth of WS2 resulted in a continuous film with metallic behaviour. These results clearly demonstrate that alkali-metal assistance is valid even in applications of gas-source CVD without oxygen-containing species, where intermediates comprising Na, W, and S can play an important role. We observed that the WS2 crystals grown by gas-source CVD exhibited a narrow size distribution when compared with crystals grown by conventional solid-source CVD, indicating that the crystal nucleation occurred almost simultaneously across the substrate, and that uniform lateral growth was dominant afterwards. This phenomenon was attributed to the suppression of inhomogeneous nucleation through the fast and uniform diffusion of the gas-phase precursors, supported by the Na-assisted suppression of the fast reactions between WF6 and H2S.

Highlights

Two-dimensional (2D) materials, such as graphene, hexagonal boron nitride and transition-metal dichalcogenides (TMDs), have gained considerable attention in recent few years, due to their electronic and optoelectronic properties[1,2,3]
The use of H2S and WF6 provide a number of additional advantages over solid precursors: i) gas-phase supply makes large-scale growth easy (e.g. WS2 chemical vapour deposition (CVD) and ALD growth from these precursors onto 300-mm Si wafers with a dielectric coating35–38); ii) they are already widely used in semiconductor manufacturing (e.g. WF6 is used for low-temperature CVD growth of W films on Si wafers to form W-plugs40–42) and iii) their high reactivity allows low-temperature WS2 growth (250–450 °C), which enhances their applicability[34,35,36,37,38,39]
We will discuss the effect of NaCl in our gas-source CVD system

Summary

Introduction

Two-dimensional (2D) materials, such as graphene, hexagonal boron nitride (hBN) and transition-metal dichalcogenides (TMDs), have gained considerable attention in recent few years, due to their electronic and optoelectronic properties[1,2,3]. We found that alkali-metal assistance method is still valid for a WS2 CVD growth form H2S and WF6 precursors: by introducing a NaCl, which is the most common alkali-metal compound into a CVD chamber, we obtained monolayer to bilayer WS2 with grain size of as large as ~10 μm on an oxidized silicon (SiO2/ Si) substrate.

Results

Conclusion