Introduction of an Al Seed Layer for Facile Adsorption of MoCl₅ during Atomic Layer Deposition of MoS₂

Abstract

A low‐temperature one‐step growth method for few‐layer MoS2 using an atomic layer deposition scheme with MoCl5 and H2S precursors is systematically studied by introducing an ultrathin Al seed layer. First, to optimize the deposition conditions, the effects of the deposition (200–420 °C) and MoCl5 canister (100–160 °C) temperatures on the MoS2 growth behavior are investigated. On the SiO2 surface, increasing the deposition temperature reduces the growth rate while favoring more lateral growth. However, an increase in the MoCl5 sublimating temperature, which is beneficial to improve the film quality, sharply reduces the growth rate, probably owing to the pronounced self‐etching effect of MoCl5. To compensate for the reduced deposition rate while maintaining the MoS2 quality, an ultrathin Al seed layer (≈5 nm) is introduced, which promotes the surface adsorption of MoCl5 molecules at an early growth stage according to density functional theory calculations. Thus, a polycrystalline mono‐to‐bilayer MoS2 film with negligible amounts of residual contaminants (particularly Cl and Al) is successfully synthesized using the proposed Al seeding approach.

Area‐Selective Atomic Layer Deposition of MoS2 using Simultaneous Deposition and Etching Characteristics of MoCl5

“…A rough surface with numerous vertical MoS 2 crystals was observed for the shortest MoCl 5 pulsing time of 1 s because of the enhanced growth by the Al seed‐layer effect. [ 26 ] However, the density of the vertical MoS 2 crystals rapidly decreased with increasing MoCl 5 pulsing time, indicating planar growth of MoS 2 at >3.5 s. The observed growth behaviors on SiO 2 and Al were also confirmed by Raman spectroscopy results shown in Figure S2, Supporting Information. As an indicator of the MoS 2 growth, the measured Raman intensities of the characteristic A 1g peaks of MoS 2 on SiO 2 and Al are plotted as a function of the MoCl 5 pulsing time in Figure 1c.…”

“…These Raman measurement results match well with the changes in the surface features shown in Figure 1a,b. As discussed in our previous report, [ 26 ] highly reactive MoCl 5 is believed to induce a self‐etching side‐effect, which led to no film deposition at prolonged MoCl 5 pulsing times. Meanwhile, according to the density functional theory calculations, [ 26 ] the adsorption energy of MoCl 5 on Al is much larger than that on SiO 2 .…”

“…Another approach is the use of precursor chemistry that provides both deposition and etching characteristics: for instance, selective epitaxial CVD growth of Si. [ 35 ] In our previous study, [ 26 ] during the development of a low‐temperature (420 °C) ALD process of MoS 2 using MoCl 5 and H 2 S, we observed an intriguing self‐etching effect when a large amount of MoCl 5 was injected by increasing its sublimating temperature. Moreover, to facilitate MoCl 5 adsorption, we introduced an Al seed layer, which enabled us to control the growth of ultrathin MoS 2 films.…”

“…However, in recent years, many research groups have been actively developing various deposition methods for producing wafer‐scale MoS 2 films for practical applications. Among these deposition methods, the ALD process using various Mo precursors [ 11–28 ] is attractive because it comprises alternating precursor injections, and thus, the adsorption characteristics of each precursor can be independently controlled.…”

“…Moreover, to facilitate MoCl 5 adsorption, we introduced an Al seed layer, which enabled us to control the growth of ultrathin MoS 2 films. [ 26 ] In this article, inspired by these unique characteristics, we propose an area‐selective ALD scheme as a bottom‐up patterning approach for MoS 2 deposition. A predefined Al pattern was used for the self‐aligned growth of MoS 2 , and the MoCl 5 pulsing time was optimized to effectively quench MoS 2 growth in situ on unwanted SiO 2 regions.…”