Surface characterization of ultrathin atomic layer deposited molybdenum oxide films using high-sensitivity low-energy ion scattering

Abstract

Few-layer, high quality, molybdenum oxide films were successfully grown using atomic layer deposition (ALD) and characterized using high-sensitivity low-energy ion scattering (HS-LEIS). The deposition quality, uniformity, and number of layers (thickness) of these films have a drastic effect on overall film properties and, therefore, on performance in electronic devices. In particular, achieving uniform and reproducible nucleation is important for creation of single-monolayer films. However, islanding often occurs during film growth in which film discontinuities or nonuniform thicknesses are formed, both of which are undesirable. We have investigated the uniformity and thickness control of molybdenum oxide films that are deposited via ALD and are precursors to MoTe2 transition metal dichalcogenides. HS-LEIS was used to assess surface coverage and islanding of thin MoOx films ranging in thickness from 0.2 nm to over 7 nm. The absence of a signal from the substrate indicated uniform nucleation and that complete surface coverage by MoOx occurred at a film thickness of approximately 0.6 nm (14 ALD cycles). Monte-Carlo-based simulations were used to predict LEIS spectra, which allowed for quantitative analysis of nucleation and film growth. These simulated spectra of few-layer films further confirmed that the grown films exhibited uniform nucleation.