Tungsten atomic layer deposition on polymers

Tungsten (W) atomic layer deposition (ALD) was investigated on a variety of polymer films and polymer particles. These polymers included polyethylene, polyvinyl chloride, polystyrene, polycarbonate, polypropylene and polymethylmethacrylate. The W ALD was performed at 80 °C using WF6 and Si2H6 as the gas phase reactants. W ALD on flat polymer films can eventually nucleate and grow after more than 60 AB cycles. X-ray photoelectron spectroscopy studies of W ALD on polystyrene after 50 AB cycles suggested that tungsten nanoclusters are present in the W ALD nucleation regime. The W ALD nucleation is greatly facilitated by a few cycles of Al2O3 ALD. W ALD films were grown at 80 °C on spin-coated polymers on silicon wafers after 10 AB cycles of Al2O3 ALD. The W ALD film was observed to grow linearly with a growth rate of 3.9 Å per AB cycle on the polymer films treated with the Al2O3 ALD seed layer. The W ALD films displayed an excellent, mirror-like optical reflectivity. The resistivity was 100–400 µΩ cm for W ALD films with thicknesses from 95–845 Å. W ALD was also observed on polymer particles after W ALD in a rotary reactor. Without the Al2O3 ALD seed layer, the nucleation of W ALD directly on the polymer particles at 80 °C required > 50 AB cycles. In contrast, the polymer particles treated with only 5 AB cycles of Al2O3 ALD were observed to blacken after 25 AB cycles of W ALD. W ALD on polymers may have applications for flexible optical mirrors, electromagnetic interference shielding and gas diffusion barriers.