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path (Figure 3). Using the SmartCut™ technology—it breaks the wafer-diameter also opportunities because in that case, III-V
technology involves first tiling III-V dies ceiling and saves scarce material because and Si devices are next to each other, which
over a 200 or 300mm silicon substrate. This only a thin layer is used rather than a bulk facilitates the interconnects.
creates a so-called pseudo-donor wafer paved substrate. This type of tiling will be the key
with dies several hundred microns thick. technology to bring these III-V materials Recent hybrid bonding D2W
Second, this pseudo-donor is used to transfer into high-volume manufacturing for display improvements
collectively thin layers (100-1,000nm) of applications, for instance. Substrates tiled The latest trends featured at ECTC 2022
III-V dies on another silicon substrate using with thin layers of III-V materials are then showed a strong interest in hybrid bonding
the SmartCut™ technology. The pseudo- provided to foundries for further device D2W. (Figures 4-5) [6–9]. Challenges
donor substrate can be reused many times. processing. In that case, III-V material of direct hybrid bonding D2W remain in
This work is underway jointly with Soitec [5]. is present at the front end of the device performance, yield and cost, which are
For applications using large III-V areas, fabrication process. This brings challenges driven by alignment capability, bonding
the SmartCut™ tiling is a breakthrough to co-process III-V materials and silicon, but quality and throughput, respectively.
Die bonder equipment is, therefore, a
key piece for industrialization; it must
meet class 1 cleanroom and accurate
surface-bonding specifications. A fruitful
collaboration between CEA-Leti and SET
Corp. enabled emergence of a die bonder
specifically designed for hybrid bonding
D2W with alignment capability of 1µm
3σ post bonding. It integrates a local clean
environment, adaptation of robotics to
avoid particulate contamination and precise
alignment thanks to its optical alignment
capability. Regarding yield, the cleaning
post dicing was the other challenge. Regular
sawing offers a simple way of dicing dies,
but it has a high level of contamination. We
have developed an efficient strategy for die
cleaning. The combination of those skills
enables demonstration of a high-yield level
and an alignment capability below <1µm
3σ (Figure 6), after bonding with high
electrical yield [8-9]. However, ensuring
a high throughput with a high bonding
precision remains a big challenge from an
economic perspective.
Before explaining the different solutions
under investigation, it is important to clarify
some definitions of alignment. Machine
Figure 2: Direct hybrid bonding cross section in W2W. SOURCE: CEA-Leti intrinsic accuracy, die placement accuracy
and die alignment post bonding are three
components of global alignment. Machine
intrinsic accuracy and die placement depend
on optics, tool parameters and environment.
The die integration characteristics and the
alignment measurement method also play
a role. Indeed, the best representation of
a misalignment is a measurement at two
extreme corners of the die. Therefore, the die
alignment post bonding depends on all of
those parameters.
An accurate alignment takes a long
time. Therefore, several approaches exist
to increase throughput based on a pick
and place (P&P) tool with increased speed
or collective bonding. Here, collective
bonding refers to pre-aligned dies with a
temporary bonding and high alignment
Figure 3: Schematic of the SmartCut™ tiling approach [5].
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