AVS 64th International Symposium & Exhibition
    2D Materials Focus Topic Wednesday Sessions
       Session 2D+EM+SS+TF-WeM

Paper 2D+EM+SS+TF-WeM2
Atomic Layer and Metalorganic Chemical Vapor Deposition of MoS2 and WS2 from bis(tert-butylimido)-bis(dialkylamido) Compounds

Wednesday, November 1, 2017, 8:20 am, Room 15

Session: 2D Materials Growth and Fabrication
Presenter: Berc Kalanyan, NIST
Authors: B. Kalanyan, NIST
J.E. Maslar, NIST
W.A. Kimes, NIST
B.A. Sperling, NIST
R. Kanjolia, EMD Performance Materials
Correspondent: Click to Email
Layered 2D transition-metal dichalcogenides (TMDs) are finding use in nanoelectronic and optoelectronic applications due to their thickness-dependent optical and electrical properties. Scalable fabrication of TMD-based devices requires vapor-phase deposition routes that can produce continuous and uniform films with sub-nanometer thickness control. Atomic layer deposition (ALD) is a desirable route for the synthesis of 2D TMDs and heterostructures due to digital thickness control achieved by sequential self-limiting surface chemistry. However, since ALD conditions are only met at relatively low deposition temperatures, most ALD films are amorphous. Some consider this a useful feature of ALD, since film growth rate and structural development can be decoupled by separating the deposition and crystallization steps. In contrast, metalorganic chemical vapor deposition (MOCVD) enables direct growth of crystalline films, but requires careful process control and precursor selection to achieve the required level of thickness control. The tradeoffs between direct CVD growth and post-sufurization and annealing of amorphous/metallic films is the focus of this work.

In this paper, we present a comparison of process characteristics and film properties, including growth rate, thickness, morphology, composition, and crystallinity, as a function of two deposition routes: ALD and MOCVD. We deposited thin films using (NtBu)2(NMe2)2M and 1-propanethiol, where M={Mo,W}, at wafer temperatures of 200°C to 400°C for ALD and 400°C to 900°C for pulsed MOCVD on SiO2/Si substrates. Precursor saturation conditions were evaluated using in situ infrared flow measurements and ex situ X-ray photoelectron spectroscopy. As-deposited and sulfur-annealed films were further evaluated using X-ray diffraction, optical spectroscopies, and microscopy. As-grown ALD films were amorphous and included a mixture of a sulfide and a conductive phase, likely a nitride. Below 300°C, deposition was limited to a thin surface oxide. Higher temperatures resulted in higher growth rates, which also introduced a weak CVD component to the growth. Deposition rates were <1.0 Å/cycle at 350°C. As-deposited films were successfully annealed to 2H-MoS2 under a sulfur atmosphere, which also removed residual nitrogen. As-grown MOCVD films were polycrystalline 2H-MoS2 at 600°C. Pulsed injections of precursor enabled Å-level control over aggregate film thickness. For both processes, wafer-scale growth and uniformity in a perpendicular flow reactor were demonstrated on 50 mm substrates. We will also present process characteristics for the analogous WS2 route and discuss initial data from MoS2/WS2 nanolaminates.