THE MICROSTRUCTURE OF REACTIVELY SPUTTERED TI-N FILMS CONTAINING THE TI2N PHASE

Titanium-nitrogen films with compositions in the two-phase regions, alpha -Ti plus epsilon -Ti//2N and epsilon -Ti//2N plus delta -TiN, were grown by radio-frequency reactive sputtering and examined using transmission electron microscopy (TEM). Films containing 30 at. % nitrogen consist of equi-axed 'grains' subdivided into alternating lamellae of alpha -Ti and epsilon -Ti//2N, with a particular orientation relationship between the two phases. Films containing 35 at. % nitrogen consist of the epsilon -Ti//2N and delta -TiN phases and have similar lamellar structure within the grains as the films with 30 at. % nitrogen. It is proposed that the films originally condense as single phase films of either alpha -Ti with nitrogen in super saturation or as single phase delta -TiN with nitrogen vacancies, and then during growth transforms to epsilon -Ti//2N via a mechanism involving a coordinated movement of titanium atoms and long-range diffusion of nitrogen.