Recess Effect Study and Process Optimization of Sub-10 μm Pitch Die-to-wafer Hybrid Bonding

To achieve fine-pitch, SOC-like I/O communication, and to realize heterogeneous integration, die-to-wafer (D2W) hybrid bonding (HB) is being investigated extensively. HB is a promising approach to extend the ability to assemble dielets at pitches well below 10 μm. Even so, the bonding mechanism with real process issues, however, has not yet been fully analyzed. In this paper, a critical comparison of HB and thermal compression bonding (TCB) is provided. The main goal of this work is to understand and alleviate three main issues in the HB process with modeling, sensitivity analysis, and experimental verification. An edge recess process is first introduced to avoid edge chipping and cracking issues during the dicing process. This increases the bond strength by 17.5%. Bonding yield is also improved after employing the edge recess process. Additionally, the effect of metal recess depth is studied in detail on sub-10 μm pads using finite element analysis (FEA), and a recess-controllable chemical mechanical planarization (CMP) parametric model is established. FEA has been combined with experimental observations to generate process windows of D2W HB. This paper provides an in-depth understanding and practical guidelines for D2W hybrid bonding.