Structure and properties of Ta–Si–N coatings obtained by pulsed magnetron sputtering

Pulsed magnetron sputtering of a TaSi2 ceramic target 120 mm in diameter was used to deposit coatings on model silicon substrates at a gas flow rate ratio of Ar/N2 = 1/2 and frequencies of 5, 50, and 350 kHz. The structure and composition of coatings were investigated using scanning electron microscopy, energy dispersive analysis and glow discharge optical emission spectroscopy. The phase composition was determined by X-ray diffraction analysis using CuKα radiation. Mechanical properties were measured by the nanoindentation method using a Nano Hardness Tester equipped with a Berkovich indenter at a load of 4 mN. The heat resistance of coatings was evaluated by isothermal annealing in the air in a muffle furnace at 1200 °С, and oxidation resistance was estimated by the structure and thickness of the oxide layer. The results of structure studies have shown that the coatings are X-ray amorphous and have a dense homogeneous structure. Increasing the frequency from 5 to 350 kHz led to a decrease in the thickness and growth rate of the coatings. Samples deposited at 5 and 50 kHz showed high mechanical performance: hardness at the level of 23–24 GPa, elastic modulus of 211–214 GPa, and elastic recovery of 75–77 %. The coating obtained at the maximum frequency had a hardness of 15 GPa, elastic modulus of 138 GPa, and elastic recovery of 65 %. Annealing led to the formation of protective SiO2, Ta2O5, TaO2 oxide layers. A pronounced crystallization of the TaSi2 phase was observed, which is confirmed by the X-ray diffraction analysis data. Samples deposited at 5 and 50 kHz showed a small oxide layer thickness of 0.9 and 1.1 μm, which indicates the good heat resistance of coatings at 1200 °С.