Self-organized lamellar structured tantalum–nitride by UHV unbalanced-magnetron sputtering

Abstract

The effect of crystal orientation and microstructure on the mechanical properties of TaNx was investigated. TaNx films were grown on a SiO2 substrate by ultrahigh vacuum unbalanced magnetron sputter deposition in mixed Ar/N2 discharges at 20 mTorr (2.67 Pa) and at 350 °C.Unlike the Ti–N system, in which TiN is the terminal phase, a large number of N-rich phases in the Ta–N system could lead to layers which had self-organized nanosized lamella structure of coherent cubic and hexagonal phases, with a correct choice of nitrogen fraction in the sputtering mixture and ion irradiation energy during growth. The preferred orientations and the microstructure of TaNx layers were controlled by varying incident ion energy Ei (=30–50 eV) and nitrogen fractions fN2 (=0.1–0.15). TaNx layers were grown on (0002)-Ti underlayer as a crystallographic template in order to relieve the stress on the films.The structure of the TaNx film transformed from B1-NaCl δ–TaNx to lamellar structured B1-NaCl δ-TaNx+ hexagonal ɛ-TaNx or B1-NaCl δ-TaNx+hexagonal γ-TaNx with increasing ion energy at the same nitrogen fraction fN2. The hardness of the films also increased by the structural change. At the nitrogen fraction of 0.1–0.125, the structure of the TaNx films was changed from δ-TaNx+ɛ-TaNx to δ-TaNx+γ-TaNx with increasing ion energy. However, at the nitrogen fraction of 0.15, the film structure did not change from δ-TaNx+ɛ-TaNx over the whole range of the applied ion energy. The hardness increased significantly from 21.1 to 45.5 GPa with increasing ion energy.