Molybdenum trioxide films have been deposited using thermal atomic layer deposition techniques with bis(tert-butylimido)bis(dimethylamido)molybdenum. Films were deposited at temperatures from 100 to 300 °C using ozone as the oxidant for the process. The Mo precursor was evaluated for thermal stability and volatility using thermogravimetric analysis and static vapor pressure measurements. Film properties were evaluated with ellipsometry, x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and secondary electron microscopy. The growth rate per cycle was determined to extend from 0.3 to 2.4 Å/cycle with <4% nonuniformity (1-sigma) with-in-wafer across a 150 mm wafer for the investigated temperature range.

Recent advances in the field of two-dimensional (2D) transition metal dichalcogenide (TMD) materials have indicated that atomic layer deposition (ALD) of the metal oxide and subsequent sulfidation could offer a method for the synthesis of large area two-dimensional materials such as MoS2 with excellent layer control over the entire substrate. However, growing large area oxide films by ALD with sub 1 nm nucleation coalescence remains a significant challenge, and the necessary steps are unexplored. In this work, we demonstrate the necessary process improvements required to achieve sub 1 nm nucleation control by characterization of nucleation domains formed by oxide deposition. Synthesis of the TMD MoS2 from sulfidation of oxide deposited by both thermal ALD from (tBuN)2(NMe2)2Mo and O3 and plasma enhanced ALD (PEALD) from (tBuN)2(NMe2)2Mo and remote O2 plasma was performed. Large uniform MoS2 areas were achieved by optimizing the effects of various growth process conditions and surface treatments on the ALD nucleation and growth of Mo-oxide and the postsulfidation of MoS2. In addition to insights into the control of the oxide deposition, film chemistry analysis during a multistep sulfidation based on less toxic sulfur as compared to H2S was performed for several temperature profiles revealing sulfur incorporation and molybdenum reduction at low temperatures but higher temperatures required for 2H crystal structure formation. The knowledge gained of the ALD, PEALD, and postsulfidation was leveraged to demonstrate tunable film thickness and centimeter-scale monolayer growth. Material quality can be studied independently of the MoS2 layer count as demonstrated by the control of the monolayer photoluminescence intensity by the temperature ramp rate during sulfidation.

Plasma-enhanced atomic layer deposition was used to grow molybdenum disulfide films using (tBuN)2(NMe2)2Mo and a remote H2S-Ar plasma as coreactants on three different substrates: thermal oxide on silicon, c-plane sapphire, and epitaxial c-plane GaN on sapphire. Depositions were carried out at 250 °C. The substrates’ effect on the growth of MoS2 was investigated through resonance Raman spectroscopy, x-ray photoelectron spectroscopy, and atomic force microscopy. In addition, transmission electron microscopy was performed on films deposited on electron-transparent silicon nitride membranes. Films of 2H-MoS2 were deposited with atomic-level control of thickness under the deposition conditions studied. By analyzing the resonance Raman spectrum, it was found that higher degrees of crystallinity could be achieved on GaN or Al2O3 substrates compared to thermally oxidized silicon.

Plasma enhanced atomic layer deposition of Al2O3 gate dielectric thin films on AlGaN/GaN substrates: The role of surface predeposition treatments

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