Effects of plasma treatment on SiO₂ aerogel film using various reactive (O₂, H₂, N₂) and non-reactive (He, Ar) gases

In order to reduce the R-C time delay of ULSI circuits, interconnection materials with low resistance and/or interlayer films with low dielectric constant should be applied. A SiO₂ aerogel film processed by spin-coating and supercritical drying has high porosity and large integral surface area. Therefore, this material can offer a low dielectric constant. In this work, we demonstrated that various gas plasma treatments can control the internal surface chemical species of SiO₂ aerogel film, such as organic groups, hydroxyl groups, and adsorbed water. Through O₂, N₂, He, and Ar plasma treatments, condensation reaction between -OR and -OH groups happened and this induced the reduction of film thickness. After the treatments, -OH related bonds were formed due to adsorbed moisture. Therefore, the dielectric constant and the leakage current increased. However, the amelioration of electrical properties could be obtained after subsequent thermal treatment. On the contrary, a H₂ plasma treated SiO₂ aerogel film showed better leakage current behavior than that of the thermally treated one. This was due to the hydrophobic character of the H₂ plasma treated sample. The H₂ plasma was seemed to passivate porous SiO₂ aerogel film with hydrogen. Then H₂ plasma treatment was revealed as one possible post-treatment of the SiO₂ aerogel film for applying to an intermetal dielectric in a multilevel interconnection structure.