Redistribution Layers (RDLs) for 2.5D/3D IC Integration

Redistribution layer (RDL) is an integral part of 3D IC integration, especially for 2.5D IC integration with a passive interposer. The RDL allows for circuitry fan-outs of and allows for lateral communication between the chips attached to the interposer. There are at least two ways to fabricate the RDL, namely (1) polymers to make the passivation and Cu-plating to make the metal layer, and (2) semiconductor back-end-of-line Cu damascene. In this study, the materials and processes of these methods are presented. Emphasis is placed on the Cu damascene method.