Self-limiting low-temperature growth of crystalline AlN thin films by plasma-enhanced atomic layer deposition

We report on the self-limiting growth and characterization of aluminum nitride (AlN) thin films. AlN films were deposited by plasma-enhanced atomic layer deposition on various substrates using trimethylaluminum (TMA) and ammonia (NH3). At 185 degrees C, deposition rate saturated for TMA and NH3 doses starting from 0.05 and 40 S. respectively. Saturative surface reactions between TMA and NH3 resulted in a constant growth rate of similar to 0.86 angstrom/cycle from 100 to 200 degrees C. Within this temperature range, film thickness increased linearly with the number of deposition cycles. At higher temperatures (>= 225 degrees C) deposition rate increased with temperature. Chemical composition and bonding states of the films deposited at 185 degrees C were investigated by Xray photoelectron spectroscopy. High resolution Al 2p and N 1s spectra confirmed the presence of AlN with peaks located at 73.02 and 396.07 eV, respectively. Films deposited at 185 degrees C were polycrystalline with a hexagonal wurtzite structure regardless of the substrate selection as determined by grazing incidence X-ray diffraction. High-resolution transmission electron microscopy images of the AlN thin films deposited on Si (100) and glass substrates revealed a microstructure consisting of nanometer sized crystallites. Films exhibited an optical band edge at similar to 5.8 eV and an optical transmittance of >95% in the visible region of the spectrum. (C) 2011 Elsevier B.V. All rights reserved.