Helium Plasma Damage of Low-k Carbon Doped Silica Film: the Effect of Si Dangling Bonds on the Dielectric Constant

The low-k carbon doped silica film has been modified by radio frequency helium plasma at 5 Pa pressure and 80 W power with subsequent XPS, FTIR and optical emission spec- troscopy analysis. XPS data indicate that helium ions have broken Si-C bonds, leading to Si-C scission with C(1s) lost seriously. The Si(2p), O(1s), peak obviously shifted to higher binding en- ergies, indicating an increasingly oxidized Si(2p). FTIR data also show that the silanol formation increased with longer exposure time up to a week. Contrarily, the CH 3 stretch, Si-C stretching bond and the ratio of the Si-O-Si cage and Si-O-Si network peak sharply decreased upon exposure to helium plasma. The OES result indicates that monovalent helium ions in plasma play a key role in damaging carbon doped silica film. So it can be concluded that the monovalent helium ions besides VUV photons can break the weak Si-C bonds to create Si dangling bonds and free methyl radicals, and the latter easily reacts with O₂ from the atmosphere to generate CO₂ and H₂ O. The bonds change is due to the Si dangling bonds combining with H₂ O, thereby, increasing the dielectric constant k value.