Low-Temperature Al2O3 Atomic Layer Deposition

Al2O3 films were deposited by atomic layer deposition (ALD) at temperatures as low as 33 C in a viscous-flow reactor using alternating exposures of Al(CH3)3 (trimethylaluminum [TMA]) and H2O. Low-temperature Al2O3 ALD films have the potential to coat thermally fragile substrates such as organic, polymeric, or biological materials. The properties of lowtemperature Al2O3 ALD films were investigated versus growth temperature by depositing films on Si(100) substrates and quartz crystal microbalance (QCM) sensors. Al2O3 film thicknesses, growth rates, densities, and optical properties were determined using surface profilometry, atomic force microscopy (AFM), QCM, and spectroscopic ellipsometry. Al2O3 film densities were lower at lower deposition temperatures. Al2O3 ALD film densities were 3.0 g\cm3 at 177 C and 2.5 g\cm3 at 33 C. AFM images showed that Al2O3 ALD films grown at low temperatures were very smooth with a root-mean-squared (RMS) roughness of only 4 (plus_minus) 1 A. Current-voltage and capacitance-voltage measurements showed good electrical properties of the lowtemperature Al2O3 ALD films. Elemental analysis of the films using forward recoil spectrometry revealed hydrogen concentrations that increased with decreasing growth temperature. No other elements were observed by Rutherford backscattering spectrometry except the parent aluminum and oxygen concentrations. Low-Atemperature l2O3 ALD at 58 C was demonstrated for the first time on a poly(ethylene terephthalate) (PET) polymeric substrate. Al2O3 ALD coatings on PET bottles resulted in reduced CO2 gas permeabilities