| The main objective of this project was to test different copper/fluoropolymer combinations as potential candidates for multilevel interconnects. The low permittivity dielectric films studied involve plasma polymerized fluorocarbons, sputtered fluoropolymers and the commercially available Teflon AF1600. These different fluoropolymer materials are compared according to their fabrication process, dielectric properties over a large frequency range, their thermal stability, and compatibility with the metallization process.; Dielectric properties, namely the permittivity and the dissipation factor, were obtained over a wide frequency range (10{dollar}sp2{dollar}-10{dollar}sp6{dollar} Hz) for metal-insulator-metal (MIM) structures which were temperature-cycled (25{dollar}spcirc{dollar}C-250{dollar}spcirc{dollar}C) under vacuum. The effect of temperature cycling on the dielectric properties was examined in order to elucidate the thermal stability and to eliminate the effect of components such as low molecular weight species, residual solvent and atmospheric contaminants. After annealing under vacuum at 200{dollar}spcirc{dollar}C, all fluoropolymer films showed a relative permittivity and dissipation factor below 2.0 and 0.001, respectively. The dielectric properties were related to the presence of free radicals and dipoles (C=O) determined by photoacoustic FTIR. The compatibility of fluoropolymers with the metallization process was analyzed by evaluating the adhesion of copper to fluoropolymers exposed to various types of heat treatments. It was found that the adhesion of copper to fluoropolymers was enhanced by preannealing in the atmosphere before copper deposition, and by postannealing in vacuum after copper deposition. The enhancement of adhesion was related to the presence of oxygen-containing groups on the surface, also determined by photoacoustic FTIR. Diffusion of copper into the polymer was revealed by X-ray photoelectron spectroscopy measurements, and it also helped to increase the copper/fluoropolymer adhesion. Suitability of fluoropolymers for the application in multilevel interconnect structures is discussed. |
