Structure, morphology and electrical properties of sputtered Zr-Si-N thin films: From solid solution to nanocomposite

DC reactive magnetron co-sputtering was used for the deposition of Zr-Si-N thin films. Si content (CSi) was varied by changing the power applied on the Si target, whereas that on Zr target was kept constant. Three series of samples have been deposited at various substrate temperatures: room temperature, 240 °C and 440 °C. The evolution of morphology, crystalline structure, grain size and lattice constant has been investigated by X-ray diffraction analyses. Nanohardness, stress and resistivity measurements provide complementary information, which validate the proposed 3-step model for the film formation of the Zr-Si-N system deposited by reactive magnetron co-sputtering. For low Si content the Si atoms substitute the Zr atoms in the ZrN lattice. Above the solubility limit, a nanocomposite film containing ZrN:Si nanocrystallites and amorphous SiNy is formed. Further increase of Si content results in a reduction of grain size (D), while the thickness of the SiNy layer at the crystallite surface remains constant. The increasing amount of the SiNy amorphous phase in the films is realized by increasing the surface to volume ratio of the crystallites. In this concentration range, the size of the crystallites in the Zr-Si-N films decreases according to the relationship CSi ∼ 1 / D. With increasing substrate temperature, the solubility limit of Si in ZrN decreases whereas the films' global nitruration (CN / (CSi + CZr)) increases. The concentration dependence of the electrical resistivity is interpreted in terms of the variation of the SiNy layer thickness.