Passivation schemes for copper/polymer thin film interconnections used in multichip modules

The use of thin inorganic dielectric films as barrier layers between copper and polyimide was examined. Emphasis was placed on discovering the effectiveness of the barrier layers in preventing copper/polyimide interaction and determining its impact on the high-frequency electrical performance of transmission line structures. The integrity of the inorganic dielectric layers as diffusion barriers for the copper was analyzed using transmission electron microscopy. These effects were studied by depositing thin layers of Si₃N ₄, SiO₂, and SiO_xN_y between chromium/copper/chromium lines and either Dow benzocyclobutene or Dupont 2525 polyimide. Both sputtered Si₃N₄ and PECVD SiO _xN_y behaved as diffusion barriers, which resulted in improved performance at very high frequencies over unprotected transmission lines