Low-Temperature Al2O3 Atomic Layer Deposition

Abstract

Al 2 O 3 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(CH 3 ) 3 (trimethylaluminum [TMA]) and H 2 O. Low-temperature Al 2 O 3 ALD films have the potential to coat thermally fragile substrates such as organic, polymeric, or biological materials. The properties of low-temperature Al 2 O 3 ALD films were investigated versus growth temperature by depositing films on Si(100) substrates and quartz crystal microbalance (QCM) sensors. Al 2 O 3 film thicknesses, growth rates, densities, and optical properties were determined using surface profilometry, atomic force microscopy (AFM), QCM, and spectroscopic ellipsometry. Al 2 O 3 film densities were lower at lower deposition temperatures. Al 2 O 3 ALD film densities were 3.0 g/cm 3 at 177 °C and 2.5 g/cm 3 at 33 °C. AFM images showed that Al 2 O 3 ALD films grown at low temperatures were very smooth with a root-mean-squared (RMS) roughness of only 4 ± 1 Å. Current−voltage and capacitance−voltage measurements showed good electrical properties of the low-temperature Al 2 O 3 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-temperature Al 2 O 3 ALD at 58 °C was demonstrated for the first time on a poly(ethylene terephthalate) (PET) polymeric substrate. Al 2 O 3 ALD coatings on PET bottles resulted in reduced CO 2 gas permeabilities.