Optimization of AlN films grown by atomic layer deposition

Abstract

AlN thin films (∼25 nm) have been grown with a Beneq TFS-200 ALD reactor on Si (111) substrates. TMA (trimethylaluminum) and NH3 were used as precursors. The substrate temperatures were 330°C, ALD cycles 550. In order to study the stoichiometry of AlN film the TMA and NH3 doses (pulses) were varied from 60 to 180 ms and from 60 to 90 ms, respectively. X-ray diffraction (XRD) data showed that the AlN films have amorphous structure. Chemical composition and bonding states were investigated by X-ray photoelectron spectroscopy (XPS). High resolution Al 2p and N 1s spectra confirmed the presence of AlN with peaks located at 73.6 and 396.8eV, respectively for all layers. Furthermore, the atomic concentration of constituent elements has been calculated from the high-resolution XPS scan. The results revealed the Al/N ratio is close to the stoichiometric value (1:1) only for AlN film grown at TMA and NH3 doses/pulses of 180 and 90 ms, respectively. AFM analysis showed that RMS roughness value for AlN films grown at TMA: NH3 pulse ratio 2:1 is about 1 nm. The results are promising in view of further studies of AlN films for SAW device application