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 (C_Si) 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 SiN_y is formed. Further increase of Si content results in a reduction of grain size (D), while the thickness of the SiN_y layer at the crystallite surface remains constant. The increasing amount of the SiN_y 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 C_Si ∼ 1 / D. With increasing substrate temperature, the solubility limit of Si in ZrN decreases whereas the films' global nitruration (C_N / (C_Si + C_Zr)) increases. The concentration dependence of the electrical resistivity is interpreted in terms of the variation of the SiN_y layer thickness.