Effects of helium ion irradiation on bubble formation in AlN/TiN multilayered system

The effects of helium ion irradiation on immiscible AlN/TiN multilayered system were studied. The structure consisted of 30 alternate AlN (~ 8 nm) and TiN (~ 9.3 nm) layers of a total thickness around 260 nm, deposited on (100) Si substrates by reactive sputtering. The system was then implanted with 30 keV He+ to very high irradiation doses, 1-4 × 1017 ions/cm2. Evaluated projected ion range was 153.1 ± 45.4 nm and maximum displacements per atom for the applied doses from 6 to 24. It was found that the multilayers remained well separated and stable after irradiation to 1 × 1017 ions/cm2, which introduces up to 10 at.% of He within the structure. The main effects were agglomeration of He bubbles around the projected ion range, mostly concentrated at the AlN edges of the interfaces, and a slight increase of the mean grain size within the affected zone. Increasing of the ion dose induced further agglomeration of bubbles, splitting of the layers at the interfaces, and final destruction of the structure. The evaluated He content was consistent with the implanted dose up to 2 × 1017 ions/cm2. For the highest dose the implanted gas is partially released from the structure. The results can be interesting towards the development of radiation tolerant materials.