Minimization of Keep-Out-Zone (KOZ) in 3D IC by local bending stress suppression with low temperature curing adhesive

Three dimensional IC (3D IC) has lots of through-Si vias (TSVs) and metal microbumps for electrical connection between stacked IC chips, and also has organic adhesives to enhance the mechanical strength of 3D IC. However, the coefficient of thermal expansion (CTE) mismatch between microbumps and organic adhesives generate the local bending stress in thinned IC chips. Therefore, Keep-Out-Zone (KOZ) for transistors must be considered in 3D IC design to eliminate characteristic fluctuations and degradations due to the local bending stress. In this study, for the first time, we evaluated the effects of low temperature curing adhesive on both the local bending stress and the resultant transistor characteristics for decrease in KOZ of 3D IC.