Effects in Surface Free Energy of Sputter-Deposited VNx Films

Abstract

Vanadium nitride (VN x ) 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. VN x thin films with VN 0.45 , VN 0.83 , VN 1.22 , VN 1.73 , VN 2.06 were prepared using a radio frequency (RF) sputter technique. The experimental results showed that the contact angle at 20 • C increases with increasing nitrogen content of the VN x films, to 101.4 • corresponding to VN 1.73 and then decreased. In addition, the contact angles decreased with increasing surface temperature, because an increase of the surface temperature disrupts the hydrogen bonds between water and the films and the water gradually vaporizes. The total surface fee energy (SFE) at 20 • C decreased with nitrogen content of the VN x films to 29.8 mN/m (VN 1.73 ) and then increased. This is because a larger contact angle means weaker hydrogen bonding which results in a lower SFE. The polar SFE component had the same trend as the total SFE, but the dispersive SFE component had the opposite trend. The polar SFE component is also lower than the dispersive SFE component. This is because hydrogen bonds are polar. The total SFE, dispersive SFE and polar SFE of the VN x films all decrease with increasing surface temperature. This is because with increasing temperature, water evaporates from the surface, disrupting hydrogen bonds and hence increasing surface entropy. The film roughness has an obvious effect on the SFE and there is tendency for the SFE to increase with increasing film surface roughness. As a result the SFE and surface roughness can be expressed in terms of a simple ratio function.

Impact of sputtering gas on the microstructural, mechanical and wetting properties of vanadium nitride coatings

“…The wettability and hydrophilicity of VN coatings were increased with the increase of N 2 partial pressure. The observed wettability properties and hydrophilicity of VN coatings were superior to the values reported so far in the literature [24,25].…”

“…There are two major factors that can affect coating's contact angle: the low surface energy and the surface roughness [38][39][40]. According to Fan et al [25], the surface free energy linearly increase with increasing surface roughness in VN coatings. In present work as the N 2 partial pressure increased to 40%, the increase in WCA could be related to appearance of highly intense crystalline plane with lower surface energy (200).…”

“…Nevertheless, it has been found that transition metal nitrides, such as TiN, ZrN, and HfN, can also be deposited with specific processing parameters to achieve superior wettability properties [23]. The research on the wettability properties of VN coatings are limited, with only a small number of studies conducted to date [24,25].…”