Growth of thin films of molybdenum oxide by atomic layer deposition

Abstract

Thin films of MoO₃ have been obtained by the atomic layer deposition (ALD) technique using molybdenum hexacarbonyl (Mo(CO)₆), ozone, and water as precursors. A window for ALD growth was found in the temperature range 152 to 172 °C. Self-limiting growth was verified at a deposition temperature of 163 °C. The upper temperature range is determined by the thermal stability of the Mo(CO)₆ precursor. The growth dynamics was further investigated by quartz crystal microbalance to determine the effect of ozone and water on the deposition process. Growth using only water as oxygen source is hardly detectable. The growth rate increases to 0.75 Å per cycle when ozone is introduced. X-ray diffraction analysis indicates that the films are amorphous as deposited, but crystallise into the α- and β-MoO₃ phases during annealing in air at 500 °C and to phase-pure, highly oriented α-MoO₃ at 600 °C. Analysis by X-ray photoelectron spectroscopy shows that both as-deposited and annealed films contain Mo(VI). Atomic force microscopy proves a very low surface roughness for as-deposited films, which becomes rather rough for annealed films. This investigation has clearly proven the capability of carbonyls as useful precursors for ALD growth of oxides.