AlN films deposited under various nitrogen concentrations by RF reactive sputtering.

Wurtzite AlN films were deposited by an RF reactive sputtering technique under various nitrogen concentrations at low temperature (350°C). The evolution of preferred orientation and morphology of the deposited films were studied by X-ray diffraction, field emission scanning electron microscopy. The vibrational phonon modes of AlN films were studied using a Fourier transform infrared (FTIR) spectrometer and a Raman spectrometer. It was found that at low nitrogen concentration, the films showed (1 0 0) preferred orientation. With increase in nitrogen concentration the films tend to be more randomly orientated as all the (1 0 0), (1 0 1), (0 0 2) peaks appeared. A further increase in nitrogen concentration resulted in c-axis (0 0 2) orientated films. The morphology of the deposited films also changed from facet to pebble-like grain structure. The formation mechanism of the preferred orientation and morphology is discussed and related to the deposition conditions. Two peaks were found in FTIR spectra and were attributed to E1(TO) and A1(TO) phonon modes. The shift of E1(TO) peak towards high wave number indicated that increased compressive stress developed in the deposited films with increase in nitrogen concentration. The major peak observed in Raman spectra was identified as being due to E22 phonon modes. The measured vibrational spectra results were related to the microstructure of the deposited films.