Structure and properties of magnetron sputtered Zr-Si-N films with a high (≥25 at.%) Si content

The Zr-Si-N films were deposited using an unbalanced dc reactive magnetron sputtering of the alloyed ZrSi₂ target in a mixture of argon and nitrogen onto steel and silicon substrates. This article reports on a systematic investigation of dependences of the structure, elemental composition, mechanical properties and oxidation resistance of Zr-Si-N films with a high (≥25 at.%) Si content on the partial pressure of nitrogen p_N2, magnetron discharge current I_d, total sputtering gas pressure p _T, substrate temperature T_s and dc and pulsed substrate bias U_s. It was demonstrated that (i) ZrSi₂ films sputtered in (a) a pure argon (p_N2=0) and (b) Zr-Si-N films sputtered at very low values of p_N2≤0.03 Pa are crystalline, electrically conductive, optically opaque and exhibit a relatively high value of the microhardness H≈17-20 GPa; (ii) Zr-Si-N films sputtered at p _N2≥0.1 Pa are X-ray amorphous, electrically insulating, optically transparent and exhibit (a) a high microhardness H of about 30 GPa and (b) a low compressive macrostress σ of about -1.2 GPa; (iii) an increase in the substrate temperature T_s from 300 to 750 °C has no effect on the structure and H of as-deposited films; the structure of the Zr-Si-N film sputtered at T_s=750 °C remains X-ray amorphous and its hardness H does not decrease with increasing T_s, i.e. it is approximately the same (≈30 GPa) as that of the film sputtered at T_s=500 °C; (iv) the Zr-Si-N films with high (≥25 at.%) Si content and high H≈30 GPa can be produced in the metallic mode of sputtering, i.e. they can be produced approximately four times faster than the binary nitrides such as, for instance, the TiN films; and (v) the Zr-Si-N films with a high (≥55 vol. %) content of the a-Si₃N₄ phase, composed of a mixture of a-Si ₃N₄+ZrN_x>1 phases, exhibit a high oxidation resistance in flowing air, greater than 1300 °C.