Abstract:Reactive magnetron sputtering was used to deposit tantalum nitride (Ta-N) thin films on Si substrate. The effect of varying the N 2 percentage in the N 2 /Ar gas mixture on the Ta-N film characteristics was investigated. Mechanical and tribological properties were studied using nanoindentation and pin-on-disc wear testing. Decreasing the N 2 content in the gas mixture was found to change the film structure from face centered cubic (fcc) TaN (from 25% to 10% N 2 ) to highly textured fcc TaN (at 7% N 2 ) to a mixture of fcc TaN 1.13 and hexagonal Ta 2 N (at 5% N 2 ), and finally to hexagonal Ta 2 N (at 3% N 2 ). A high hardness of about 33 GPa was shown by the films containing the hexagonal Ta 2 N phase (5% and 3% N 2 ). Decreasing the N 2 content below 7% N 2 was also found to result in microstructural refinement with grain size 5-15 nm. Besides the highest hardness, the film deposited with 3% N 2 content exhibited the highest hardness/modulus ratio (0.13), and elastic recovery (68%), and very low wear rate (3.1 × 10 −6 mm 3 ·N −1 ·m −1 ).

Tantalum silicon nitride (Ta–Si–N) films were synthesized on Si substrate via magnetron sputtering. The structure and properties of the Ta–Si–N films were investigated as a function of the N2 content in the N2/Ar gas mixture. Increasing the N2 percentage in the gas mixture from 7% to 20% changed the film structure from textured hexagonal (hex) Ta2N to nontextured hex Ta2N to a mixture of face-centered cubic (fcc) TaN and hex Ta2N, and finally to fcc TaN. X-ray photoelectron spectroscopy showed Ta–N and Si–N bonds in the films. The film microstructure was found to change from columnar morphology with visible amorphous boundaries (at 13% N2) to columnar morphology with absence of amorphous boundaries (at 15% N2). Increasing N2 content increased hardness in the films with those deposited with 13–15% N2 displaying the highest hardness of ~40 ± 2 GPa. In addition, the 13% N2 films showed a ratio of H/E* > 0.11, elastic recovery of ~60%, low coefficient of friction of 0.6, reduced wear rate (7.09 × 10−6 mm3/N·m), and remained thermally stable up to 800 °C. The results suggest that the Ta–Si–N films have high potential as hard tribological nanocomposite coatings.

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