Page 13 - Chip Scale Review Sep Oct_2022-digital

Figure 4: D2W process flow. SOURCE: CEA-Leti

Figure 5: Die-to-wafer. SOURCE: CEA-Leti;
COURTESY: P. Jayet
accuracy. The final bonding is then
performed collectively by W2W. The Figure 6: Direct hybrid bonding cross section in D2W. SOURCE: CEA-Leti
alignment is then composed of combined
D2W and W2W misalignment errors. The
throughput is then limited by the P&P tool
used for die placement of the temporary
bonding. This solution seems to be limited
to solve the D2W throughput issue.
One alternative strategy developed by
CEA-Leti in collaboration with Intel is
self-assembly (Figure 7). A gross pre-
alignment >200µm is performed, while the
fine alignment is realized by a water droplet
and capillarity forces. This process can be
implemented either in collective, or in P&P
ways. In the collective way, dies are placed in
a holder with a high-speed die sorter at low
precision >200µm. All dies are then picked-
up simultaneously by droplets and self-
aligned. In the P&P, pre–alignment can be
coarse enough to reach high throughput. The
droplet completes the fine alignment to reach
below 400nm 3σ. The throughput could be
improved up to 2,000 dies/hour. Dedicated
self-assembly equipment needs to be
developed in collaboration with equipment
suppliers to ensure reproducibility for high- Figure 7: a) Self-assembly process flow; b) self-assembly principle—water droplet used for fine alignment
volume manufacturing. thanks to capillary forces. SOURCE: CEA-Leti

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