Multichip-to-Wafer Three-Dimensional Integration Technology Using Chip Self-Assembly With Excimer Lamp Irradiation

Self-assembly of multichips with metal microbump electrodes is demonstrated by using water surface tension to increase the stacking throughput/yield and chip alignment accuracy of conventional chip-to-wafer 3-D integration. Three-dimensional microbump interconnects are formed by self-assembly with thermal compression at 200
$^{\circ}\hbox{C}$
. Chips with In–Au microbumps with pitches of 10 and 20
$\mu\hbox{m}$
are tightly bonded to Si wafers after the flip-chip self-assembly process, resulting in high alignment accuracies of 0.8 and 0.2
$\mu\hbox{m}$
in the
$x$
- and
$y$
-directions, respectively. Selective hydrophilization by 172-nm excimer lamp irradiation gives a high wettability contrast between hydrophilic chip bonding areas and hydrophobic surrounding areas on the wafers. This assists high-precision multichip self-assembly. A 2500-In–Au-microbump daisy chain is formed with a yield of 100% by flip-chip self-assembly, and it exhibits ohmic contact. The resistance is sufficiently low for 3-D large-scale integration application, being comparable to that obtained by conventional mechanical chip alignment.