Wafer Level Back to Back Hybrid Bonding for Multiple Wafer Stacking

This paper describes the demonstration of a 4-layer wafer stack using a combination of face-to-face and back-to-back, wafer-to-wafer hybrid bonding process. Details of process flow, process characterization and challenges in multi-layer wafer stacking are included in this paper. Wafer warpage of different pattern density is simulated with 3D finite element analysis (FEA) model. Wafer bow results match with low warpage results of simulation. 4-layer wafer was stacked together without separation. The process development and improvement carries out.