Advances in Photosensitive Polymer Based Damascene RDL Processes: Toward Submicrometer Pitches With More Metal Layers

In this study, we demonstrate the scaling potential of our damascene redistribution layer (RDL) approach by manufacturing an RDL process using a photosensitive polymer and copper metal lines with a target pitch of 1 μm. Among the various advantages of using a photosensitive dielectric and a damascene approach, the presence of a chemical-mechanical polishing (CMP) step after the copper growth process is key to guarantee the flatness of the stack. Ultimately, it allows for more RDL layer to be patterned at resolution limits. This approach is demonstrated by processing a 4 metal layers RDL with a minimal pitch of 3.2 μm. Collected electrical data as well as FIB cross-sections and SEM imaging performed after various process steps confirm the excellent patterning of the metal wires thus demonstrating the superiority of the damascene approach compared to the semi-additive process.