Electron beam enhanced multilayering and planarization in preimidized polyimides

High-density packaging and interconnection applications frequently involve the use of polyimide-based materials as interlevel dielectrics for multilevel interconnection schemes. Surface planarity after each polymer layer is very important to the fabrication of multilayer structures. Highly nonplanar surfaces were observed in a multilayer test structure, fabricated using a thermally cured polyimide (Ultradel 7501). In this study, the effect of a novel cure technique involving electron beam (e-beam) exposure on multilayering and planarization behavior in Ultradel 7501 is investigated. Planarization measurements were conducted on different feature sizes and at various locations on the wafer in order to investigate the effect of solvent exposure, time and area of contact between multiple layers. The degree of planarization was found to improve from -206% for a thermally cured case to +15% for an e-beam cured sample. Analysis of the solvent induced polymer swelling and its effect on multilayer planarization of Ultradel 7501 is presented.