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

Abstract

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°C, deposition rate saturated for TMA and NH3 doses starting from 0.05 and 40s, respectively. Saturative surface reactions between TMA and NH3 resulted in a constant growth rate of ~0.86Å/cycle from 100 to 200°C. Within this temperature range, film thickness increased linearly with the number of deposition cycles. At higher temperatures (≥225°C) deposition rate increased with temperature. Chemical composition and bonding states of the films deposited at 185°C were investigated by X-ray photoelectron spectroscopy. High resolution Al 2p and N 1s spectra confirmed the presence of AlN with peaks located at 73.02 and 396.07eV, respectively. Films deposited at 185°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 ~5.8eV and an optical transmittance of >95% in the visible region of the spectrum.