Nucleation and Growth during Al2O3 Atomic Layer Deposition on Polymers

Abstract

Nucleation and growth during Al 2 O 3 atomic layer deposition (ALD) were explored on a variety of polymer films at 85 °C. Al 2 O 3 ALD was performed using sequential exposures of Al(CH 3 ) 3 [trimethylaluminum (TMA)] and H 2 O. 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. Al 2 O 3 ALD during the sequential TMA and H 2 O 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 Al 2 O 3 ALD. Following the initial nucleation period, linear Al 2 O 3 ALD growth was observed on all the polymers. The thickness of the Al 2 O 3 ALD films was also characterized by ex situ surface profilometry. Based on the QCM measurements and recent FTIR measurements of Al 2 O 3 ALD on low-density PE, a model is proposed for Al 2 O 3 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 H 2 O exposure. This model for Al 2 O 3 ALD does not require specific chemical groups on the polymer surface to initiate Al 2 O 3 ALD. This model should be valuable to understand and optimize the use of these Al 2 O 3 ALD films as seed layers and gas diffusion barriers on polymers.