Damage originating from plasma processing is a persistent problem with porous ultra-low-k dielectric films, such as SiCOH. Although most of the proposed mechanisms of plasma-induced damage focus on the role of ion bombardment and radical attack, vacuum ultraviolet (VUV) photons have been shown to play a role in bond modification of this material [1]. Using a vacuum beam apparatus with a calibrated VUV lamp, we show that 147 nm VUV photons cause bond scissioning in SiCOH, resulting in subsequent, post-exposure adsorption and reaction of water vapor from the atmosphere. Furthermore, the level of damage increases significantly under simultaneous exposure to VUV photons and O2. The role of photodissociation (and O radical formation) is shown to be negligible for the experimental conditions. The vacuum beam photon exposures are representative of typical plasma processes. Fourier-transform infrared (FTIR) spectroscopy implies that O2 itself reacts with photo-generated Si radical sites, replacing scissioned Si-C bonds with Si-O bonds (and ultimately SiOH groups) and making the surface more hydrophilic than with photon exposure alone. The present results demonstrate that VUV photo-generated surface reactions can be potent contributors to ultra-low k dielectric SiCOH film plasma-induced damage, and suggest that they could play analogous roles in many other plasma-surface interactions.

 

[1] Jinnai, B. et al., Damage Mechanism in low-dielectric (low-k) films during plasma processes. Journal of Vacuum Science & Technology B, 2008, 26(6): p. 1926.