Corrosion Resistance of Atomic Layer Deposition-Generated Amorphous Thin Films

Atomic layer deposition (ALD) was used to prepare amorphous thin films of Al₂O₃, Nb₂O₅, and Ta₂O₅ on both silicon substrates and aluminum blocks. Etch rates in 10 M NH₄OH were determined from X-ray reflectometry data collected as a function of time. Amorphous Al₂O₃ thin films were found to have an etch rate of 0.5 nm min^-1 and an increase in roughness of ∼0.01 nm min^-1. Electron microscopy data showed etch pits, consistent with the increase in roughness. Amorphous Nb₂O₅ and Ta₂O₅ films showed no appreciable etching or roughening over the course of a ∼500 h continuous immersion. An Nb₂O₅-coated aluminum block showed no corrosion after immersion in 10 M NH₄OH for over 200 h, suggesting that the coatings were pinhole-free. These results suggest that amorphous ALD thin films of Nb₂O₅ and Ta₂O₅ are candidates as barrier layers for aluminum in caustic environments.