A study on D2W Hybrid Cu bonding Technology for HBM Multi-die Stacking

Hybrid copper bonding technology (HCB) has been widely studied in the field of high-bandwidth memory (HBM) due to its multiple advantages such as power efficiency, density, speed, bandwidth, and heat dissipation, and allows direct connection with Cu pad. Chemical Mechanical Polishing(CMP) process that determines Cu pad dishing is critical to achieve reliable interconnections between chips. Actually, un-bonded Cu-Cu pads were observed in high dishing pads and interface voids were observed at high protrusion pads. However, Cu pad quality has dramatically changed after CMP process through the wafer level processing such as WSS, thinning, cleaning, and annealing process. Thus, analyzing the Cu dishing changes during the process and the behavior of Cu pad at high temperature is crucial for reliable connection between pads. In this study, the behavior of Cu pad and the factors affecting dishing were investigated using Atomic Force Microscopy(AFM). We investigated the effect of the BEOL structure on the behavior of Cu pad and oxide which adjacent to Pad at high temperature. We analyzed the changes in Cu pad dishing after CMP due to cleaning solutions and thermal treatments of the wafer. By reflecting the analysis results, we adjust the dishing quality considering the structure and other processes. With this study, we can accurately predict the dishing target and demonstrate 16H HBM applied HCB technology successfully.