Material Optimization of Permanent and Temporary Adhesives for Wafer-level Three-dimensional Integration

Permanent and temporary adhesives have been developed for the fabrication of multi-layer stacks using ultra-thin wafers of a few micrometers or less. The material properties required for thinning and bonding of 300 mm wafers in the wafer-on-wafer (WOW) process are: (1) thermal stability of the adhesive in the wafer stacking process, and (2) matching of the operating temperatures of the temporary and permanent adhesives. Here, the performance of permanent and temporary adhesives is described. Previously, the rigid body pendulum method was used to measure the material viscosity of the permanent and temporary adhesives to determine the temperature conditions for the wafer bonding and thermal de-bonding processes. In this paper, the possibility of mechanical de-bonding of the temporary adhesive at room temperature is reported. Furthermore, the performance of the permanent adhesive was evaluated with respect to thermal resistance for outgassing and weight loss under high-temperature conditions, as well as thermal cycling test resistance under conditions other than those previously reported.