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

Abstract

We have developed permanent and temporary adhesives that are suitable for fabricating multilevel stacks using ultra-thin wafers of several micrometers or less for wafer-on-wafer (WOW) technology with bumpless dual-damascene interconnects (via-last after bonding). The hot-melt type temporary adhesive had a bonding temperature of around 130 °C and a de-bonding temperature of over 200 °C. After the de-bonding process, residual temporary adhesive was removed by using a conventional solvent. The permanent adhesive had a low curing temperature of around 135-170 °C and high heat resistance (maximum operating temperature, 300 °C). By using this permanent adhesive, vertical through-silicon via interconnects with low contact resistivity and fine uniformity were demonstrated by optimizing the WOW process by using a bottom cleaning process. In this paper, the characteristics of these permanent and temporary adhesives are described. For the temporary adhesive residue, which was considered to consist of hydrocarbon compounds, a uniform distribution on the de-bonding wafer washed with PGME was observed, and the thickness of the residue was estimated to be 1-2 nm. The permanent adhesive exhibited adhesion to SiO2 and Si with highly reliable TCT resistance, and a good etching profile. The solid state of the permanent adhesive coated on an Si substrate exhibited no diffusion in the SIMS profile. From the I-V curve, the permanent adhesive exhibited a current density of 10-9 to 10-8 A/cm2 at -400 to 400 MV/cm, indicating that it was a near-perfect electrical insulator.