Atmospheric-pressure spatial chemical vapor deposition of tungsten oxide

Abstract

Atmospheric-pressure spatial atomic layer deposition (AP-SALD) and atmospheric-pressure spatial chemical vapor deposition (AP-SCVD) are rapid, open-air techniques for the deposition of conformal, pinhole-free films over large areas. In this work, a precursor nebulizer and an ozone generator are incorporated into an AP-SALD system to enable the deposition of tungsten oxide (WO3) films by AP-SCVD. The precursors bis(t-butylimido) bis(dimethylamino) tungsten(VI) and ozone are used with a film deposition temperature of 350 °C to achieve a growth per cycle of 1.2 Å/cycle. A bandgap of 3.26 eV and a refractive index of 2.36 were obtained, consistent with the previous reports for WO3 films. The pinhole-free films were found to be a mixture of hexagonal and monoclinic WO3, with an increasing monoclinic nature after annealing. Additionally, the as-deposited film was substoichiometric with an O/W ratio of 2.3, which increased to 2.36 after annealing at 450 °C. The successful open-air deposition of tungsten oxide via the incorporation of a precursor nebulizer and ozone generator paves the way for large-area deposition of tungsten oxide for commercial applications.