Coupling capacitance in face-to-face (F2F) bonded 3D ICs: Trends and implications

Face-to-face (F2F) is a bonding style in three-dimensional integrated circuits (3D ICs) that bonds ICs by using the top-metal (face) as the bonding side when stacking two ICs. As technology scales in F2F bonding, the distance between the ICs becomes as small as few microns. Due to this shorter distance, significant coupling occurs between these ICs. In this paper, we investigate the impact of coupling capacitance when ICs are bonded in a F2F manner. Using a field-solver-based modeling methodology, we examine three critical areas related to F2F parasitics: (1) physical and process factors that impact F2F coupling capacitance, (2) capacitance error when inter-die interactions are not considered, and (3) the impact of micro-bumps on F2F capacitance. The results indicate that F2F separation distances smaller than 10 microns will lead to significant inter-die capacitive interactions that must be considered when extracting F2F bonded 3D ICs.