Effects of N2-content on formation behavior in AlN thin films studied by NEXAFS: Theory and experiment

Abstract In this work, AlN thin films were deposited on glass slides by a reactive-radio frequency (RF) magnetron sputtering with various mixed ambient of N2/(Ar + N2) flow ratio at 20%, 40%, 60% and 80%. X-ray diffraction (XRD) investigation showed (0002) plane of wurtzite-AlN for 60% and 80% of N2/(Ar + N2). In contrast, samples with 20% and 40% of N2/(Ar + N2) could not exhibit the clear peak of the (0002) plane because of the low level of AlN crystal structure on glass slides. However, the near edge X-ray absorption fine structure (NEXAFS) spectra at nitrogen K-edge showed the evolution of thin film growth and local environment at the initial state of crystal’s formation. The results were compared with calculated NEXAFS spectra obtained from the FEFF9 program and first-principles calculations, in which the density functional theory (DFT) was employed to calculate formation energy. An excellent agreement between the experiment and calculation on the formation mechanism was revealed. The AlN thin films were seen to exhibit a preferred orientation along the a, b-axis and the c-axis at low and high N2/(Ar + N2) ratio of ambient gas, respectively. This result was also confirmed with the surface morphology observed by AFM and SEM.