Materials Transactions Online

Materials Transactions, Vol.48 No.09 (2007) pp.2449-2453
© 2007 The Japan Institute of Metals

Surface Free Energy Effects in Sputter-Deposited WNx Films

Chun-Wei Fan and Shih-Chin Lee

Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan, R. O. China

WNx thin films have attracted much attention for semiconductor IC packaging molding dies and forming tools due to their excellent hardness, thermal stability. WNx thin films with WN0.46, WN1.03, WN1.52, WN1.91, WN2.54 were prepared using radio frequency (RF) sputtering. The experimental results showed that the contact angle at 20°C go up with raising N2 content to 116.7° at beginning, corresponding to WN1.91, 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, Diiodomethane, Ethylene glycol and the films and these liquids vaporize gradually. The total SFE at 20°C decrease with N2 content to raise to 37.6 mN/m(WN1.91) at the start, and then increase. 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 WNx films decreased with increasing surface temperature. This is because liquids evaporation on the surface, disrupted hydrogen bonds and surface entropy increasing with increasing temperature. The film roughness has an obvious effect on the SFE and there is tendency for the SFE to increase with increasing film surface roughness. Because SFE and surface roughness can be expressed as a function in direct ratio.

(Received 2007/4/26; Accepted 2007/6/12; Published 2007/8/25)

Keywords: Surface free energy, Contact angle, WNx

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