Development of Resins for Bumpless Interconnects and Wafer-On-Wafer (WOW) Integration

Our permanent and temporary adhesives are suitable for wafer-on-wafer (WOW) technology using ultrathin wafer multilayer stacks with bumpless dual damascene interconnects.. Because our temporary adhesive is a reactive hot-melt type, the bonding temperature is around 130 °C and the de-bonding temperature is higher than the bonding temperature (>200 °C). After de-bonding and washing processes, the temporary adhesive residue was uniformly distributed on the de-bonding wafer, and the thickness of the residue was estimated to be 1-2 nm in a secondary ion mass spectrometry (SIMS) profile. A permanent adhesive with high heat resistance (maximum operating temperature, 300 °C) was prepared and could be cured at 135-170 °C, which is lower than the de-bonding temperature of the temporary adhesive. The permanent adhesive exhibited adhesion to SiO
₂
and Si with highly reliable thermal cycle test (TCT) resistance, and a good etching profile. The solid state of the permanent adhesive coated on an Si substrate exhibited no diffusion in a SIMS profile. The electrochemical ability of the permanent adhesive is indicated by its current density of 10
^-9
to 10
^-8
A/cm
²
at -400 to 400 MV/cm, indicating that it is a near-perfect electrical insulator. Vertical through-silicon via interconnects were demonstrated by optimizing the WOW process using our two adhesives.