Roles of hydrogen on the composition and bonding of atoms in hydrogenated aluminum nitride films prepared by RF reactive sputtering

AlN films are of interest as piezoelectric materials for high frequency surface acoustic wave (SAW) devices due to the high phase velocity. A correct stoichiometry as well as low concentrations of impurities such as oxygen are important because nonstoichiometry or impurities in the films create a leakage current between the input and output interdigital transducer (IDT) of SAW filters. This, in turn, acts as noise in the filtering characteristics. The roles of hydrogen on the composition and bonding of atoms in hydrogenated aluminium nitride (AlN:H) films were studied. The AlN:H films were prepared by rf magnetron sputtering of an Al target in a Ar/N2/H2 gas mixture. The bonding characteristics of Al, N, O, and H atoms were analysed by XPS and FTIR. The film composition and activation energy for the evolution of H2 gas from the film were determined by Rutherford backscattering spectrometry and gas chromatography, respectively. With increasing H2 content in the gas mixture, the contents of nitrogen increased but those of oxygen decreased in the film because hydrogen facilitates bonding with unbound nitrogen and hinders nitrogen-oxygen bonding. The activation energy for the evolution of H2 gas from AlN:H films was found to be 0.11 plus or minus 0.02 eV, implying that the hydrogen in the film formed a hydrogen bond. 13 refs.