Changes in material properties of low-k interlayer dielectric polymers induced by exposure to plasmas

We have studied the effects of plasma treatments on the electrical, chemical and mechanical properties of fluorinated-poly-arylene-ether (FLARE) and divinylsiloxane-benzocyclobutane (BCB) polymers for use as low dielectric-constant (k) interlayer dielectrics in complementary metal-oxide-Si (CMOS). It is observed that plasma treatments induce anisotropy in k, which becomes more pronounced in FLARE. Also following the exposures, FLARE is rendered mechanically harder, whereas BCB becomes electrically leakier and the leakage current is significantly reduced by annealing in forming gas (6% H₂ and 94% N₂) at 350 °C for 30 min. These observations are explained in terms of polymer scissioning and cross-linking processes that are caused by plasma-polymer interaction mechanisms. These mechanisms include: (i) ion bombardment, (ii) ultra-violet radiation, and (iii) plasma charging. The latter mechanism is suggested to dominate the plasma-polymer interaction.