Formation of (Ti,Al)N∕Ti2AlN multilayers after annealing of TiN∕TiAl(N) multilayers deposited by ion beam sputtering

By using ion beam sputtering, TiN∕TiAl(N) multilayers of various modulation wavelengths (Λ=8, 13, and 32nm) were deposited onto silicon substrates at room temperature. After annealing at 600°C in vacuum, one obtains for Λ=13nm a (Ti,Al)N∕Ti2AlN multilayer as it is evidenced from x-ray diffraction, high resolution transmission electron microscopy, and energy filtered electron imaging experiments. X-ray photoelectron spectroscopy (XPS) experiments show that the as-deposited TiAl sublayers contain a noticeable amount of nitrogen atoms which mean concentration varies with the period Λ. They also evidenced the diffusion of aluminum into TiN sublayers after annealing. Deduced from these observations, we propose a model to explain why this solid-state phase transformation depends on the period Λ of the multilayer.