Ti–Al–Si–N films for superhard coatings deposited by reactive cosputtering using Ti, Al, and Si targets

Ti–Al–Si–N films with various composition ratios were deposited by a specially designed cosputtering system with three magnetron cathodes by controlling the impressed power ratios on each cathode independently. All the films were deposited on Si wafers at $300°C$ under a total gas pressure of $0.5Pa$ with a nitrogen flow ratio $[N2∕(N2+Ar)]$ of 70% using Ti, Al, and Si targets. Hardness and Young’s modulus normal to the surface of the Ti–Al–Si–N films were analyzed by nanoindentation equipped with a Berkovich diamond indenter. It was clarified that the hardest condition of the films with different $Ti∕Al$ ratios could be obtained when the Si content was about $10–20at.%$⁠, whereas the maximum values of the hardness did not depend on the Al content. Nanocomposite structures where Ti–Al–N or Ti–Al–Si–N nanocrystallites were embedded in an amorphous $Si3N4$ matrix were clearly observed by transmission electron microscopy which must contribute largely on the hardening of the films. The size of the nanocrystallites for the hardest film was about $25nm$⁠. On the other hand, the solid solution of Al atoms into $TiNx$ was not so effective in the Ti–Al–Si–N films. The hardest film of the Ti–Al–Si–N system in this study was $Ti0.77Al0.06Si0.17Nx$ with a hardness of $34GPa$⁠.