Rapid Growth of Crystalline Mn₅O₈ by Self-Limited Multilayer Deposition using Mn(EtCp)₂ and O₃

Abstract

This work investigates the use of ozone as a post-treatment of ALD-grown MnO and as a coreactant with bis(ethylcyclopentadienyl)manganese (Mn(EtCp)2) in ALD-like film growth. In situ quartz crystal microbalance measurements are used to monitor the mass changes during growth, which are coupled with ex situ materials characterization following deposition to evaluate the resulting film composition and structure. We determined that during O3 post-treatment of ALD-grown MnO, O3 oxidizes the near-surface region corresponding to a conversion of 22 Å of the MnO film to MnO2. Following oxidation by O3, exposure of Mn(EtCp)2 results in mass gains of over 300 ng/cm(2), which exceeds the expected mass gain for reaction of the Mn(EtCp)2 precursor with surface hydroxyls by over four times. We attribute this high mass gain to adsorbed Mn(EtCp)2 shedding its EtCp ligands at the surface and releasing Mn(II) ions which subsequently diffuse into the bulk film and partially reduce the oxidized film back to MnO. These Mn(EtCp)2 and O3 reactions are combined in sequential steps with (a) Mn(EtCp)2 reacting at the surface of an O-rich layer, shedding its two EtCp ligands and freeing Mn(II) to diffuse into the film followed by (b) O3 oxidizing the film surface and withdrawing Mn from the subsurface to create an O-rich layer. This deposition process results in self-limiting multilayer deposition of crystalline Mn5O8 films with a density of 4.7 g/cm(3) and an anomalously high growth rate of 5.7 Å/cycle. Mn5O8 is a metastable phase of manganese oxide which possesses an intermediate composition between the alternating MnO and MnO2 compositions of the near-surface during the Mn(EtCp)2 and O3 exposures.

Manganese(II) Molecular Sources for Plasma-Assisted CVD of Mn Oxides and Fluorides: From Precursors to Growth Process

“…[4][5]16 Among the different synthetic routes to manganese-based nanosystems, 6,17 chemical vapor deposition (CVD) and atomic layer deposition (ALD) hold a significant promise for the tailored fabrication of high quality films and nanoarchitectures. 1,[18][19][20] Nevertheless, the successful development of CVD/ALD synthetic protocols is directly dependent on the availability of volatile precursors, ensuring a reproducible mass supply and endowed with clean decomposition/fragmentation patterns. [21][22] So far, only a few reports on the preparation of MnF2 layers by ALD 23 and CVD 8 are present in the literature, whereas most studies have been dedicated to the synthesis of supported Mn oxide systems.…”

“…In this context, several molecular precursors have been proposed and tested, encompassing different manganese bis(amidinates), 18,24 bis(ethylcyclopentadienyl)manganese 1,23,25-29 and various -diketonates, as, for instance, Mn(dpm)3 (Hdpm = 2,2,6,6-tetramethyl-3,5-heptanedione), [2][3]30 Mn(acac)2(H2O)2 (Hacac = 2,4pentanedione), 20 and Mn(hfa)2(H2O)2. 31 Some of these works have reported on the formation of Mn(II), 29 Mn(III) oxides, 2 Mn5O8, 1 as well as Mn3O4 3,32 and MnO2. 3 In most of these studies, the authors report on the formation of unspecified MnOx systems.…”

The Influence of Ozone: Superstoichiometric Oxygen in Atomic Layer Deposition of Fe2O3 Using tert‐Butylferrocene and O3

“…The phase dependence on ozone exposure can be used both to tune the phase between the pure γ phase and pure α phase and to control the orientation of crystalline domains. Other ALD processes relying on ozone as a coreactant may also exhibit similar behaviors, possibly including our preliminary work on NiO ALD and the study of MnO ALD by Young et al [ 70 ] Additionally, this mechanism may affect growth and behavior of ternary ALD systems by introducing reactive surface oxygen species that could influence the precursor chemisorption. Further investigation of these phenomena and more detailed mechanistic studies are the subject of future work.…”

Understanding and Utilizing Reactive Oxygen Reservoirs in Atomic Layer Deposition of Metal Oxides with Ozone

“…Also similar to findings for NiO and Fe2O3, the authors reported an increase in oxygen content in MnOx corresponding to changes in oxide stoichiometry, high exposures needed to reach saturation, and film phase conversion. 55 On the contrary, deposition of aluminum oxide from trimethylaluminum and ozone does not seem to exhibit this behavior, instead saturating at a sub-monolayer GPC with much lower reactant exposures. 34,35 The presence of the oxygen reservoir phenomenon in some ozone-based, metal oxide ALD processes but not others raises the question of what chemical, material, and process properties are necessary to cause this subsurface reactive oxygen growth.…”