Exploring Al2O3 blister evolution through cathodoluminescence and attenuated total reflectance infrared analyses

This work focuses on the morphological and optical evolution of Al2O3 thick films grown by atomic layer deposition on Si-SiO2 substrates. Blister formation has been the subject of extensive research in the literature; our work fills a crucial gap in the optical characterization of areas inside and outside blisters. Morphological studies were carried out by scanning electron microscopy; we found a reciprocal relationship between the density of the blisters and their diameter. The thickness and refractive index were studied by ellipsometry, revealing a systematic increase in the refractive index with increasing annealing temperature. In addition, we observed the hydrophobic behavior in all films using the water contact angle technique, which suggests that even with blisters, this material can be used in waterproof coatings. Using Auger spectroscopy, we confirmed that delamination occurs completely once the blisters are broken. In this work, we perform cathodoluminescence measurements outside and inside the ampoules. In the area outside the blisters, we observe emissions attributed to the F centers, and the change from the main peaks of 2.8 and 3.4 eV for the as-deposited film to the dominance of emissions centered at 3.4 and 3.7 eV is clearly observed. Furthermore, we observed a strong increase in the cathodoluminescence signal at higher annealing temperatures. On the other hand, we also observed the evolution of the blisters through the cathodoluminescence spectra; in that area, we observed the radical change in the spectrum once the blister is broken, giving rise to the SiO2 signals. We also observed this rupture through a new absorption band in the attenuated total reflectance IR spectra.