Effects of annealing on the electrical and optical properties of AlNxOy thin films

Abstract

Aluminium oxynitride is known to be a ceramic material with high strength and hardness, resulting from a stabilization of alumina (Al2O3) with nitrogen, in a cubic spinel structure, at thermodynamic conditions very different from those found in low plasma temperature deposition processes. Beyond this stable phase of AlNxOy, the available knowledge on this system is still very reduced and the interest on studding this material arises from the fact that it may combine some of the advantages of the three base systems, Al, AlN and Al2O3, by changing the concentration of aluminium, oxygen and nitrogen in the films. In fact, recent studies showed that AlNxOy thin films deposited by physical vapour deposition presents unusual changes in the growing morphology and structure that may be quite different from those of spinel, consisting of Al nanoparticles embedded in an amorphous AlNxOy matrix. Depending on the amount of oxygen and nitrogen in the matrix, a wide variation in the electrical properties, as well as peculiar optical responses, such as an unusual large broadband absorption for some films, can be found in the samples. In this work, the thermal stability of representative AlNxOy coatings was tested in vacuum, using annealing temperatures ranging from 200 to 800ºC. No significant changes in the Al-type structure were observed for annealing temperatures of up to 600 ºC, below the aluminium melting point. On the contrary, for higher temperatures, new crystalline phases were found, which resulted in significant changes in the optical properties, and gradual changes in the values of electrical resistivity.