Nucleation and Growth during Al2O3 Atomic Layer Deposition on Polymers

Nucleation and growth during Al2O3 atomic layer deposition (ALD) were explored on a variety of polymer films at 85 °C. Al2O3 ALD was performed using sequential exposures of Al(CH3)3 [trimethylaluminum (TMA)] and H2O. The polymer films were polystyrene (PS), polypropylene (PP), poly(methyl methacrylate) (PMMA), polyethylene (PE), and poly(vinyl chloride) (PVC). These polymer films were prepared by spin-coating onto the surface of a quartz crystal microbalance (QCM) sensor or the surface of a Si(100) wafer. Al2O3 ALD during the sequential TMA and H2O exposures was monitored in situ on the various polymers using the QCM. The QCM measurements revealed distinct differences for each polymer in the initial nucleation period during Al2O3 ALD. Following the initial nucleation period, linear Al2O3 ALD growth was observed on all the polymers. The thickness of the Al2O3 ALD films was also characterized by ex situ surface profilometry. Based on the QCM measurements and recent FTIR measurements of Al2O3 ALD on low-density PE, a model is proposed for Al2O3 ALD nucleation and growth on polymers. This model is based on the adsorption of TMA onto the surface and absorption into the near-surface region of the polymer. The adsorbed and absorbed TMA is then available for subsequent reaction with the H2O exposure. This model for Al2O3 ALD does not require specific chemical groups on the polymer surface to initiate Al2O3 ALD. This model should be valuable to understand and optimize the use of these Al2O3 ALD films as seed layers and gas diffusion barriers on polymers.