Atomic layer deposition and post-growth thermal annealing of ultrathin MoO3 layers on silicon substrates: Formation of surface nanostructures

• Published in: Applied surface science Vol. 439; pp. 583 - 588
• Main Authors: Liu, Hongfei, Yang, Ren Bin, Yang, Weifeng, Jin, Yunjiang, Lee, Coryl J.J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2018
• Subjects: Atomic evaporation and diffusion; Atomic layer deposition; MoO3 ultrathin film; Surficial melting; Thermal annealing; MoO3 ultrathin film; Atomic layer deposition; Thermal annealing; Atomic evaporation and diffusion; Surficial melting
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2018.01.082

•MoO3 ultrathin films have been grown by ALD on Si at 120 °C.•Annealing at Tann = 550 and 750 °C leads to surface particles and TCL structures.•XPS reveals MoO3 and its compositions reduce with increasing Tann.•EDX reveals Mo in the TCL structures rather than the TCL-free areas.•A possible growth process of TCL on the surface of SiO2 is proposed. Ultrathin MoO3 layers have been grown on Si substrates at 120 °C by atomic layer deposition (ALD) using molybdenum hexacarbonyl [Mo(CO)6] and ozone (O3) as the Mo- and O-source precursors, respectively. The ultrathin films were further annealed in air at Tann = 550–750 °C for 15 min. Scanning-electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy have been employed to evaluate the morphological and elemental properties as well as their evolutions upon annealing of the thin films. They revealed an interfacial SiOx layer in between the MoO3 layer and the Si substrate; this SiOx layer converted into SiO2 during the annealing; and the equivalent thickness of the MoO3 (SiO2) layer decreased (increased) with the increase in Tann. Particles with diameters smaller than 50 nm emerged at Tann = 550 °C and their sizes (density) were reduced (increased) by increasing Tann to 650 °C. A further increase of Tann to 750 °C resulted in telephone-cord-like MoO3 structures, initiated from isolated particles on the surface. These observations have been discussed and interpreted based on temperature-dependent atomic interdiffusions, surface evaporations, and/or melting of MoO3, which shed new light on ALD MoO3 towards its electronic applications.