Fabrication of Intra-level Extended Air-Gaps using the harder Sacrificial Polymer Placeholder for Ultra Low-k Dielectrics

摘要

The role of elastic modulus of the sacrificial polymer in forming Air-gap structures for intra-level, ultra low-κ interconnects was investigated. Air-gaps using the sacrificial polymer placeholder in the intra-level dielectric (EMD), the mechanical and thermal properties of the sacrificial polymers are critical for process reliability and yield. In order to improve the process reliability, a harder sacrificial polymer was characterized and compared to the previous sacrificial polymer in terms of mechanical and thermal properties using nanoindentation, image processing, thermal gravimetric analysis (TGA), and contact angle measurement. Using the harder sacrificial polymer, air-gaps/Cu interconnect structures were fabricated. In addition, air-gaps were extended into the inter-level dielectric (ILD) layer in order to further decrease the effective dielectric constant (k_(eff)) of the interconnect structures. The measured effective dielectric constant of air-gaps/Cu and extended air-gaps/Cu interconnect structures were 2.42 and 2.17 respectively. The moisture uptake of extended air-gaps/Cu interconnects was also investigated. Exposure of the extended air-gaps/Cu interconnect to hexamethyldisilazane (HMDS) vapor was found to successfully remove moisture and make the air-gaps/Cu interconnect more hydrophobic.