Wafer Warpage Characterization of Multi-layer Structure Composed of Diverse Passivation Layers and Re-Distribution Layers for Cost-Effective 2.5D IC Packaging Alternatives

Conventional IC packaging requires chips to be packaged at the same level, while newly developed 2.5D/3D IC packaging utilizes skyscraper approach to stack various types of chips with diverse functions occupying similar footprint, not only reducing overall package dimension, but also improving electrical interconnection performance. The major difference between 2.5D/3D IC lies in the implementation of medium wafer with Through Silicon Via (TSV) technology, often referred to as Through Silicon Interposer (TSI). Numerous concepts have been proposed to further reduce the cost on TSI fabrication, and the necessity of utilizing TSI has also been reconsidered. One of the most recent approaches is to change the role of TSI from a permanent interconnection medium to a temporary medium with only interconnection portion retained. In order to achieve this, temporary carrier is attached during early stage of process, and Epoxy Molding Compound (EMC) is implemented as supporter at another side in later stage of process. The above approach utilizes multi-layer structure composed of passivation layers and Re-Distribution Layers (RDL) on a temporary carrier as frontside process supporter, and compound molding process is implemented to support backside process after the removal of frontside carrier mentioned herein. In order to make the molding process feasible, the material properties and behaviors of this multi-layer structure should be investigated and characterized in details. Polyimide (PI) and Polybenzoxazole (PBO) have always been crucial to the packaging industry as passivation materials, providing the benefits of great isolation, stress buffering, copper compatibility, and so forth. In this research, we have particularly focused on studies regarding how these organic passivation films interact with RDL in warpage performance aspect from materials point of view. Certain crucial factors have been investigated for their effects on warpage change, and the relationship between warpage and these factors were elaborated and discussed in this paper. From the obtained warpage results, carrier CTE, passivation material types, and the number of passivation layers, all showed apparent effects on warpage change. With these findings, wafer warpage of the entire structure composed of passivation layers and RDL can be characterized, not only offering comprehensive knowledge about thin wafer warpage tuning, but also contributing to the realization of cost-effective 2.5D IC packaging alternatives without the requirement of TSI.