Die-level Via-last TSV formation and Heterogeneous 3D Integration with Multi-Project Wafers Using Photosensitive Temporary Adhesives for Agile Prototyping

This work presents a die-level, via-last integration methodology that transforms standard two-dimensional dies from multi-project wafer shuttle services into vertically integrated structures. A major challenge in die-level processing is maintaining sub-micron placement accuracy during high-temperature steps; conventional thermoplastic adhesives soften and cause severe die shifts that ruin lithographic overlay. To solve this issue, we develop a highly stable temporary bonding process using a B-staged photosensitive polyimide. Optimized at 200°C, the polyimide balances high heat resistance with high cleanability with solvent when debonding. During chemical vapor deposition for the formation of the through-Si via (TSV) liner dielectric at 200°C, this adhesive limits die displacement to less than 0.7 µm, dramatically outperforming conventional thermoplastics. Leveraging this stable platform, TSVs with a 10-μm diameter and a 4:1 aspect ratio are successfully formed on singulated dies. Cross-sectional analysis confirms void-free Cu electroplating and continuous isolation liners, validating a precise, cost-effective workflow for democratizing three-dimensional heterogeneous integration with additional TSV processing.