Structural and optical properties of c-axis oriented aluminum nitride thin films prepared at low temperature by reactive radio-frequency magnetron sputtering

Spectroscopic ellipsometry, X-ray diffraction and transmission electron microscopy experiments are employed to characterize aluminum nitride (AlN) thin films obtained by radio-frequency magnetron sputtering at low temperature (≈ 50 °C). To understand the growth mechanism and to get in depth information of such films by using ex situ characterization techniques, the AlN thin film sample series were prepared for different sputtering times, while keeping constant all the other deposition conditions. The diffraction studies reveal a [002] oriented growth of the AlN thin films. The misorientation of this crystallographic axis to the normal to the surface reduces progressively with film growth. A nonmonotonic behavior of the AlN pseudo-refractive index versus deposition time indicates a complex depth profile of the AlN thin films optical properties. The difference in orientation dispersion of the [002] crystallite axis, the variation of defects concentration and each constituent atom density influence the refractive index evolution. Our interpretation validity was verified by producing and characterizing samples obtained at intermediate deposition time. The AlN thin films show also very good pull-out adherence values.

► Aluminum nitride (AlN) films are obtained by reactive magnetron sputtering.
► Synthesis process is conducted at low temperature.
► The refractive index is dependent on structural anisotropy and defect concentration.
► The AlN thin films c-axis orientation improves by increasing the film thickness.
► The AlN film crystallinity improves gradually by increasing the film thickness.