Effects in Surface Free Energy of Sputter-Deposited MoNx Films

Abstract

MoNx thin films have attracted much attention for semiconductor IC packaging molding dies and forming tools due to their excellent hardness, thermal stability. MoNx thin films with MoN0.57, MoN0.96, MoN1.48, MoN2.07, MoN2.44 were prepared using radio frequency (RF) sputter. The experimental results showed that the contact angle at 20 °C go up with raising N2 content to 106.4° at beginning, corresponding to MoN2.07, and then drop off. In addition, the contact angle components decreased with increasing surface temperature. Because increasing surface temperature disrupts the hydrogen bonds between water and the films and water vaporize gradually. The total surface free energy (SFE) at 20 °C decreases with N2 content to raise to 33.8 mN/m (MoN2.07) at the start, and then increases. Because a larger contact angle means that a weaker hydrogen bonding, resulting in a lower SFE. The polar SFE component has same trend with total SFE, but the dispersive SFE component is on the contrary exactly. The polar SFE component is also lower than the dispersive SFE component. This is resulting from hydrogen bonding being polar. The total SFE, dispersive SFE, and polar SFE of MoNx films decreased with increasing surface temperature. This is because water evaporation on the surface, disrupted hydrogen bonds and surface entropy increasing with increasing temperature.