Influence of the nitrogen fraction on AlN thin film deposited by cathodic arc ion

Abstract

Thin films of aluminum nitride (AlN) have been grown, using the cathodic arc ion deposition technique. The effects of nitrogen fractions in the discharge on synthesized films growth rate, stoichiometric ratio (N/Al), crystal orientation and molecular mode of vibration have been investigated. AlN films have been studied by means of Rutherford backscattering (RBS) spectroscopy, X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), scanning electron microscope (SEM) and the four probe method. In RBS results, it has been found that growth rate and stoichiometric ratio decrease while reducing the nitrogen content in the synthesized chamber. XRD patterns indicated that films prepared in 100–85% nitrogen condition exhibit mixed phase of wurtzite+FFC, with preferential orientation along (002) corresponding to the hexagonal phase. It also demonstrated that at lower nitrogen environment, the transformation from mixed phase of wurtzite+FCC to a single phase of FCC–AlN occurs. FTIR spectroscopic analysis was employed to determine the nature of chemical bonding and vibrational phonon modes. Its spectra depicted a dominant peak around 850cm−1 corresponding to the longitudinal optical (LO) mode of vibration. A shift in the LO mode peak toward lower wavenumbers was noticed with the decrease of nitrogen fraction, illustrating the decline of nitrogen concentration in the deposited AlN films. The 75% nitrogen fraction appeared critical for AlN film properties, such as shifting of mixed (wurtzite+FCC) phase to single FCC–Al(N), a sharp drop of stoichiometric ratio and deposition rate. Measurements of resistivity recorded by the four probe method depicted a sharp decline in the corresponding growth condition.