Study on the copper/polymer hybrid bonding using benzocyclobutene (BCB) polymer with chemical mechanical polishing (CMP) method

Abstract

In order to miniaturize chips and process big data, research on 2.5D/3D packaging to realize light, thin and compact semiconductor devices is being actively conducted. This can be realized through High Bandwidth Memory (HBM), which dramatically increases the bandwidth of stacked memory devices using Through Silicon Vias (TSV) bonded by micro-bump inside the chip. Currently, Sn/Ag solder is used for stable bonding due to a low melting point, but it is difficult to secure an ultra-fine pitch of less than 10 μm due to the bridging effect and side wall wetting. To solve this problem, Cu direct bonding technology through Direct Bond Interconnect (DBI) using SiO2 is being developed. However, SiO2-SiO2 bonding has a low adhesion strength compared to the existing polymer-based bonding, and is highly dependent on the process temperature and time Therefore, in this study, we conducted a systematic study on polymer-based Cu bonding technology with high reliability. We analyzed the material properties of benzocyclobutene (BCB) and successfully performed Cu direct bonding through an optimized chemical mechanical polishing (CMP) process. In conclusion, we were able to improve structural stability by developing a Cu/polymer hybrid CMP process and high-reliability Cu-Cu bonding technology.