Reaction-induced phase separation from supersaturated solid solution to nitride in thin films

For the development of an advanced fabrication process aimed for nano-structured coating, a combination process of ion beam sputtering (IBS) and ion implantation has been conducted on Ti-X-N films. Non-equilibrium Ti-V and Ti-Si films have been prepared by IBS, and then followed by N⁺ implantation into the films to investigate low-temperature reaction-induced nano-phase separation in ternary Ti-V-N and Ti-Si-N systems. Ti-12 at.% V and Ti-20 at.% Si have been deposited on (001)Si substrate with thickness 150 nm by IBS. The structural change due to the N-implantation has been evaluated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) measurements. The cross-sectional TEM images of the as-deposited films respectively show nano-crystalline bcc Ti-V and amorphous Ti-Si. N-implantation with a dose of 5.0 × 10¹⁷ ion/cm² induces affected zones consisting of equi-axed grains on the surface of the Ti-Si and Ti-V films. The selected area diffraction pattern (SAED) from the affected zone shows the direct formation of fcc-TiN during N-implantation. The N concentration has been measured by the XPS depth profiling. The N concentration in Ti-V and Ti-Si films are ∼30 at.% N average and 60 at.% N maximum. The compositional gradient of N against the depth of the film suggested that the introduction of equi-axed grains was mainly due to the chemical reaction of Ti-N in proportion to the N concentration. The decreasing of Si concentration in Ti-Si film during N-implantation suggests that the segregation of Si might simultaneously occur with the preferential nitriding of Ti. The structural difference between N-implanted Ti-V and Ti-Si is mainly attributed to the difference in miscibility of V and Si into TiN.