High temperature behavior of reactively sputtered AlN films on float glass substrates

Abstract

Thin AlN films were deposited on the air side of float glass substrates by reactive direct-current magnetron sputtering of an aluminum target in Ar–N2 gas mixtures, and at 4 kW of power. These films were characterized by transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy (XPS). For nitrogen partial flow rates fN2, of 0.3 or higher, and for thicknesses of up to 800 Å, the gas composition does not affect the composition and morphology of the as-deposited films significantly. On the other hand, the morphology of films deposited on float glass and heated in air to 700 °C has a strong dependence on the composition of the working gas: films that are formed at low values of fN2 craze, while those deposited at high N2 partial pressures remain continuous upon heating but develop a wavy morphology. XPS/inert gas depth profiling analyses of the coated float glass samples revealed the formation of a thin layer with an N/Al ratio less than that of the as-deposited film at the interface, suggesting the interfacial oxidation of the film by the float glass substrate, as well as strong film–substrate adhesion. While the sputtering conditions influence the morphology of the heated samples, the high thermal expansion coefficient of the soda-lime-silica float glass, and its viscous flow, appear to be the cause of film deformations at high temperatures. Also upon heating, a graded oxy–nitride layer forms on the surfaces of these films. The thickness of both of the above oxidized layers depends on the temperature and duration of the heating schedule.