Effects in Surface Free Energy of Sputter-Deposited TaNx Films

摘要

TaNx thin films have attracted much attention for semiconductor integrated circuit (IC) packaging molding dies and forming tools due to their excellent hardness and thermal stability. Tantalum nitride (TaNx) thin films with TaN$_{0.63}$, TaN$_{1.14}$, TaN $_{1.58}$, TaN$_{2.19}$ , and TaN$_{2.81}$ were prepared using radio frequency (RF) sputter. The experimental results showed that the contact angle at 20 $^{circ}$ C go up with raising ${rm N}_{2}$ content to 119.2$^{circ}$ at beginning, corresponding to TaN $_{1.58}$, 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 $^{circ}$C decrease with ${rm N}_{2}$ content to raise to 39.6 mN/m(TaN$_{1.58}$) at the start, and then increase. A larger contact angle means 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 results from hydrogen bonding being polar. The total SFE, dispersive SFE, and polar SFE of TaNx films decreased with increasing surface temperature. This is because water evaporation on the surface, disrupted hydrogen bonds, and surface entropy increase with increasing temperature. The film roughness has an obvious effect on the SFE and there is a tendency for the SFE to increase with increasing film surface roughness. SFE and surface roughness can be expressed as a function in direct ratio.