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

Abstract

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. © 2006 Elsevier B.V. All rights reserved.