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Molecular Layer Deposition of Organic and Hybrid Organic-Inorganic Films

Conformal polymeric films can be grown by a sequential, self-limiting surface chemistry process known as molecular layer deposition (MLD) that is very similar to atomic layer deposition (ALD). The MLD reactants are typically monomers for step-wise condensation polymerization and can yield completely organic or hybrid organic-inorganic alloys. Our previous work has demonstrated polyamide film growth using MLD. Nylon 66 MLD has been accomplished using adipoyl chloride and 1,6-hexanediamine as the reactants. Kevlar [Poly(p-Phenyleneterephthalamide)] MLD has been performed using terephthaloyl chloride and 1,4-phenylene diamine as the reactants. In situ FTIR studies have revealed that the MLD surface chemistry is self-limiting and sequential exposures of the reactants lead to linear film growth. Our more recent work has focused on the growth of hybrid organic-inorganic films. This research has concentrated on a new class of polymers known as alucones. One alucone is grown using trimethylaluminum (TMA) and ethylene glycol (EG). The growth of alucone poly(aluminum ethylene glycol), [AlOCH2CH2O]n, using the sequential exposures of TMA and EG is shown in the adjacent figure. Alucone films were fabricated on silicon substrates at temperatures ranging from 85 °C to 175 °C. In situ quartz crystal microbalance and ex situ x-ray reflectivity experiments confirmed the linear growth of the alucone film versus number of TMA/EG reaction cycles at all temperatures. The MLD growth rates decreased at higher temperatures. Growth rates were 4 A per cycle at 85 C and 1.7 A per cycle at 135 C. In situ and ex situ FTIR were used to monitor the surface reactions. Ex situ FTIR and XPS were used to determine the chemical composition of the bulk films.