Investigations on the oxidation of zirconium nitride films in air by nuclear reaction analysis and backscattering spectrometry

The thermal oxidation of dc magnetron sputter deposited thin ZrN films in air in the temperature range of 100-475 °C has been studied by depth profiling N using nuclear reaction analysis (NRA) involving 15N(1H,αγ)12C resonance reaction and O using 3.05 MeV 16O(α,α)16O resonant scattering. The structural and morphological changes accompanying the process have also been investigated. NRA/backscattering spectrometry measurements show that oxidation results in the formation of ZrO1.8±0.1 at the surface. An interface consisting of Zr, O and N is also formed underneath the surface oxide. For an isothermal annealing, oxide layer as well as interface exhibits parabolic growth with the duration of annealing. The diffusion of oxygen through the already grown oxide layer (D = 5.6 × 10−14 cm2 s−1 at 475 °C) forms the rate-controlling step of oxidation. The diffusion may be facilitated by the high concentration of oxygen vacancies in the oxide layer. Glancing incidence X-ray diffraction (GIXRD) measurements indicate that zirconia films formed are phase-singular (monoclinic) and are textured in (2 0 0) and (3 1 1) orientations. Examination by scanning electron microscopy (SEM) reveals the formation of blisters on sample surfaces on prolonged oxidation. The blistering can be attributed to intrinsic growth stress arising due to the larger molar volume of zirconium oxide in comparison to zirconium nitride, a fact demonstrated by the depth profile measurements as well.