Characterization of AIN thin films annealed by CO₂ laser

AIN is wurtzite structure material with the largest direct band gap (6.2 eV) in III-V compound. It possesses excellent properties of thermal conductivity, surface acoustic wave velocity, piezoelectric coefficient, chemical stability and high refractive index. These characteristics make it be a proper material for applications of surface acoustic wave (SAW) device, UV optoelectronic device, high electron mobility transistor, high frequency and power device, etc. Compared with conventional tube furnace (CTF) and rapid thermal annealing (RTA) method, the rapid localized heating process of scanning focused CO₂ laser beam can reduce thermal expansion, lattice mismatch and film cracks issues caused in CTF and RTA annealing process. From the X-ray diffraction (XRD) ω scan results, the FWHMs of rocking curve are decreased and prove the improvement of AIN films c-axis crystallinity quality after CO₂ laser annealing. From the atomic force microscopy (AFM) results, the roughness of samples after CO₂ laser annealing don't have any obviously decay and prove that CO₂ laser annealing can avoid causing crack and poorer surface roughness of AIN / sappire and AIN / Si (111) films. The results of ellipsometer show the refractive indices of AIN films after CO₂ laser annealing are increasing. Indicating CO₂ laser annealing improving the compactness of AIN films. All these results show CO₂ laser annealing for AIN films will be a good method to improve its properties and reduce any possible negative effects. (author)