Formation of composite ternary nitride thin films by magnetron sputtering co-deposition

Thin films of M–X–N (M stands for early transition metal and X = Si, Ge, Sn) are studied as protective coatings. To extend the knowledge about the formation of nanocomposite films, various M–X–N systems have been compared. Ti–Si–N, Ti–Ge–N, Ti–Sn–N, Nb–Si–N, Zr–Si–N and Cr–Si–N thin films were deposited by reactive magnetron sputtering, from confocal targets in a mixed Ar/N2 atmosphere. The chemical reactivity of germanium and tin with nitrogen is significantly lower than that of Si and Ti. Therefore, the Ti–Ge–N and Ti–Sn–N systems are different from Ti–Si–N. Important changes in the morphology and structure of M–X–N films are induced by X addition. Nanocrystalline composite films are formed in all these investigated ternary systems.As a function of increasing X content (CX), the size of the crystallites D in the Ti–Si–N, Ti–Ge–N, Nb–Si–N and Zr–Si–N films decreases (from tens of nm to 2 nm) following the relationship CX ∼ 1 / D. The segregation of X atoms on the MN crystallite surface is responsible for the limitation of their growth. It results in the formation of a SiNy or TiGey amorphous phase on the crystallite surfaces. In the case of Nb–Si–N and Zr–Si–N systems, Si atoms can substitute metal atoms in the cubic MN lattice up to a critical concentration (solubility limit). Ti–Si–N, Ti–Ge–N and Ti–Sn–N systems are different: no solubility of Si, Ge and Sn in the TiN lattice is observed. For every composite film, the morphology changes result in a maximum hardness value at a typical concentration 2 ≤ CX ≤ 12 at.%. Resistivity measurements provide experimental mean for determining the limit of Si solubility in M–Si–N ternary systems and for following the thickness evolution of the SiNy coverage layer in the composite films.