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 spectroscopy 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 energies, 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 CH3 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 O-2 from the atmosphere to generate CO2 and H2O. The bonds change is due to the Si dangling bonds combining with H2O, thereby, increasing the dielectric constant k value.