Two-dimensional (2D) transition metal dichalcogenides are potential low dissipative semiconductor materials for nanoelectronic devices. Such applications require the deposition of these materials in their crystalline form and with controlled number of monolayers on large area substrates, preferably using growth temperatures compatible with temperature sensitive structures. This paper presents a low temperature Plasma Enhanced Atomic Layer Deposition (PEALD) process for 2D WS2 based on a ternary reaction cycle consisting of consecutive WF6, H2 plasma and H2S reactions. Strongly textured nanocrystalline WS2 is grown at 300 °C. The composition and crystallinity of these layers depends on the PEALD process conditions, as understood by a model for the redox chemistry of this process. The H2 plasma is essential for the deposition of WS2 as it enables the reduction of-W 6+ Fx surface species. Nevertheless, the impact of sub-surface reduction reactions needs to be minimized to obtain WS2 with well-controlled composition (S/W ratio of two).

is, graphene, transition metal dichalcogenides (TMDs), [ 2,3 ] topological insulators, [ 4 ] h-BN [ 5 ] and h-AlN, [ 6 ] as well the recent phosphorene, [ 7 ] silicene, [ 8 ] and germanene [ 9 ] provide the ability to control the channel thickness at atomic level. This characteristic translates into improved gate control over the channel barrier and into reduced short-channel effects, thus paving the way toward ultimate miniaturization and new device concepts. Recently, 2D transition metal dichalcogenides, have proven to be promising candidates for electronics and optoelectronic applications. [10][11][12][13][14][15][16] From a pioneering perspective, the availability of TMDs with different work functions and band structures guarantees a great potential for band gap engineering of heterostructures. These systems are fundamentally different and more fl exible than traditional heterostructures composed of conventional semiconductors. In particular, due to the weak interlayer interaction, a TMD molecular layer grows from the beginning with its own lattice constant forming an interface with reduced amount of defects. The relaxed lattice matching condition permits to combine almost any layered material and create artifi cial heterojunctions with designed band alignment. 2D heterostructures

We demonstrate the impact of reducing agents for Chemical Vapor Deposition (CVD) and Atomic Layer Deposition (ALD) of WS2 from WF6 and H2S precursors. Nanocrystalline WS2 layers with a two-dimensional structure can be obtained at low deposition temperatures (300-450 °C) without using a template or anneal.

The H2S sulfurization of metal and metal oxide molybdenum films and the H2 influence on their morphology is described.

Despite rapid progress in 2D molybdenum disulfide (MoS) research in recent years, MoS field-effect transistors (FETs) still suffer from a high metal-to-MoS contact resistance and low intrinsic mobility, which are major hindrances to their future application. We report an efficient technique to dope thin-film MoS FETs using a poly(vinyl-alcohol) (PVA) polymeric coating. This results in a reduction of the contact resistance by up to 30% as well as a reduction in the channel resistance to 20 kΩ sq. Using a dehydration process, we were able to effectively control the surface interactions between MoS and the more electropositive hydroxyl groups (-OH) of PVA, which provided a controllable and yet reversible increase in the charge carrier density to a value of 8.0 × 10 cm. The non-covalent, thus non-destructive, PVA doping of MoS increases the carrier concentration without degrading the mobility, which shows a monotonic increase while enhancing the doping effect. The PVA doping technique is then exploited to create heavily doped access regions to the intrinsic MoS channel, which yields 200% increase of the ON-state source-drain current. This establishes PVA doping as an effective approach to enhance the transport properties of MoS FETs for a variety of applications.

The cleaning of two-dimensional (2D) materials is an essential step in the fabrication of future devices, leveraging their unique physical, optical, and chemical properties. Part of these emerging 2D materials are transition metal dichalcogenides (TMDs). So far there is limited understanding of the cleaning of “monolayer” TMD materials. In this study, we report on the use of downstream H2 plasma to clean the surface of monolayer WS2 grown by MOCVD. We demonstrate that high-temperature processing is essential, allowing to maximize the removal rate of polymers and to mitigate damage caused to the WS2 in the form of sulfur vacancies. We show that low temperature in situ carbonyl sulfide (OCS) soak is an efficient way to resulfurize the material, besides high-temperature H2S annealing. The cleaning processes and mechanisms elucidated in this work are tested on back-gated field-effect transistors, confirming that transport properties of WS2 devices can be maintained by the combination of H2 plasma cleaning and OCS restoration. The low-damage plasma cleaning based on H2 and OCS is very reproducible, fast (completed in a few minutes) and uses a 300 mm industrial plasma etch system qualified for standard semiconductor pilot production. This process is, therefore, expected to enable the industrial scale-up of 2D-based devices, co-integrated with silicon technology.

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Porous organosilicate glass thin films, with k-value 2.0, were exposed to 147 nm vacuum ultra-violet (VUV) photons emitted in a Xenon capacitive coupled plasma discharge. Strong methyl bond depletion was observed, concomitant with a significant increase of the bulk dielectric constant. This indicates that, besides reactive radical diffusion, photons emitted during plasma processing do impede dielectric properties and therefore need to be tackled appropriately during patterning and integration. The detrimental effect of VUV irradiation can be partly suppressed by stuffing the low-k porous matrix with proper sacrificial polymers showing high VUV absorption together with good thermal and VUV stability. In addition, the choice of an appropriate hard-mask, showing high VUV absorption, can minimize VUV damage. Particular processing conditions allow to minimize the fluence of photons to the substrate and lead to negligible VUV damage. For patterned structures, in order to reduce VUV damage in the bulk and on feature sidewalls, the combination of both pore stuffing/material densification and absorbing hard-mask is recommended, and/or the use of low VUV-emitting plasma discharge.