Properties of magnetron sputtered Al–Si–N thin films with a low and high Si content

The article reports on properties of Al–Si–N films with a low (≤ 10 at.%) and high (≥ 25 at.%) Si content reactively sputtered using a closed magnetic field dual magnetron system operated in ac pulse mode. The films were sputtered from a composed target (a Si plate fixed by an Al ring with inner diameter Øi = 15 or 26 mm). Main attention was devoted to the investigation of a relationship between the structure of the films and their mechanical properties, thermal stability of hardness, and oxidation resistance. It was found that (1) while the films with a low (≤ 10 at.%) Si content are crystalline (c-(Al–Si–N)), those with a high (≥ 25 at.%) Si content are amorphous (a-(Al–Si–N)) when sputtered at the substrate temperature Ts = 500 °C, (2) both groups of the films exhibit (i) a high hardness H = 21 and 25 GPa, respectively, and high values of the oxidation resistance exceeding 1000 °C; 1100 °C (Δm = 0 mg/cm2) and 1300 °C (Δm ≈ 0.003 mg/cm2), respectively, (3) the hardness of a-(Al–Si–N) does not vary with increasing annealing temperature Ta up to 1100 °C even after 4 h, and (4) a high oxidation resistance of c-(Al–Si–N) film with a low (< 10 at.%) Si content is due to the formation of a dense, nearly amorphous Al2O3 surface layer which is formed in reaction of free Al atoms with ambient oxygen and prevents the fast penetration of oxygen into bulk of the film. Obtained results contribute to understand the effect of Al and Si in the Al–Si–N thin film on its mechanical properties, thermal stability and oxidation resistance.