Development of High Modulus Temporary Bonding Material for 2.5D/3D IC Integration

In an attempt to resolve the cracking and chipping issues of edge trimming wafer during back grinding, a newly developed high modulus temporary bonding material (TBM) with high glass transition temperature (Tg) was developed in this paper. Its specific rheological properties, such as high modulus at room temperature as well as low viscosity at bonding temperature, which enables the bonding pair to survive the whole temporary bonding and debonding (TBDB) process. The 12-inch wafer pair was bonded at 220°C and 30 kN pressure for 5 min, and the warpage (0.35 mm) is small enough to be negligible. After bonding, back grinding and a subsequent CMP process were successfully achieved. The device wafer with the adhesive layer edge together was reduced to 70 µm, and there were no chipping or breakage observed at the edges due to its high mechanical strength. Besides, a series of backside processes, such as PVD, reflow soldering simulation and wet process were conducted on the wafer pair, and there were no voids or bubbles found due to its superior thermal and chemical resistance. And the ultra-thin wafer pair was successfully separated with UV laser ablation. Finally, the adhesive was completely cleaned off with a commercial cleaning solvent by optical microscope observation.