Al2O3 and TiO2 Atomic Layer Deposition on Copper for Water Corrosion Resistance

Al2O3 and TiO2 atomic layer deposition (ALD) were employed to develop an ultrathin barrier film on copper to prevent water corrosion. The strategy was to utilize Al2O3 ALD as a pinhole-free barrier and to protect the Al2O3 ALD using TiO2 ALD. An initial set of experiments was performed at 177 degrees C to establish that Al2O3 ALD could nucleate on copper and produce a high-quality Al2O3 film. In situ quartz crystal microbalance (QCM) measurements verified that Al2O3 ALD nucleated and grew efficiently on copper-plated quartz crystals at 177 degrees C using trimethylaluminum (TMA) and water as the reactants. An electroplating technique also established that the Al2O3 ALD films had a low defect density. A second set of experiments was performed for ALD at 120 degrees C to study the ability of ALD films to prevent copper corrosion. These experiments revealed that an Al2O3 ALD film alone was insufficient to prevent copper corrosion because of the dissolution of the Al2O3 film in water. Subsequently, TiO2 ALD was explored on copper at 120 degrees C using TiCl4 and water as the reactants. The resulting TiO2 films also did not prevent the water corrosion of copper. Fortunately, Al2O3 films with a TiO2 capping layer were much more resilient to dissolution in water and prevented the water corrosion of copper. Optical microscopy images revealed that TiO2 capping layers as thin as 200 angstrom on Al2O3 adhesion layers could prevent copper corrosion in water at 90 degrees C for similar to 80 days. In contrast, the copper corroded almost immediately in water at 90 degrees C for Al2O3 and ZnO films by themselves on copper. Ellipsometer measurements revealed that Al2O3 films with a thickness of similar to 200 angstrom and ZnO films with a thickness of similar to 250 angstrom dissolved in water at 90 degrees C in similar to 10 days. In contrast, the ellipsometer measurements confirmed that the TiO2 capping layers with thicknesses of similar to 200 angstrom on the Al2O3 adhesion layers protected the copper for similar to 80 days in water at 90 degrees C. The TiO(2)ALD coatings were also hydrophilic and facilitated H2O wetting to copper wire mesh substrates.