Effect of the microstructure of Si 3N 4 on the adhesion strength of TiN film on Si 3N 4

Abstract

The effect of the microstructure of silicon nitride, which was used as a substrate, on the adhesion strength of physical vapor deposited TiN film on Si 3N 4 was investigated. Silicon nitride substrates with different microstructures were synthesized by controlling the size (fine or coarse), the phase (α or β) of starting Si 3N 4 powder, and sintering temperature. The microstructure of Si 3N 4 was characterized in terms of grain size, aspect ratio of the elongated grain, and β-to-α phase ratio. For a given chemical composition but different mechanical properties, such as toughness, elastic modulus, and hardness of Si 3N 4 were obtained from the diverse microstructures. Hertzian indentation was used to estimate the yield properties of Si 3N 4, such as critical loads for yield ( P y) and for ring cracking ( P c). The effect of the microstructure of Si 3N 4 on adhesion strength evaluated by scratch test is discussed. TiN films on Si 3N 4 showed high adhesion strengths in the range of 80–140 N. Hardness and the P y of Si 3N 4 substrate were the primary parameters influencing the adhesion strength of TiN film. In TiN coating on Si 3N 4, substrates with finer grain sizes and higher α phase ratios, which show high hardness and high P y, were suitable for higher adhesion strength of TiN film.