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There are several D2W bonding methods available for The bonder should be capable of achieving sub-micron
heterogeneous integration, each with its own advantages alignment accuracy, and should also be able to handle
and disadvantages, as shown in Table 1. Selecting the best a high volume of dies for efficient production. The next
approach for a given application depends on factors such as die step involves transferring the dies from the carrier wafer
size, thickness, total stack height, and interface considerations to the product wafer. This is typically achieved through
like contact design and density. W2W bonding using high-precision alignment and bonding
equipment. The bonding process should be performed under
controlled conditions to ensure uniformity and reliability.
After the dies have been transferred to the product wafer,
the die carrier is debonded and removed. This involves
separating the adhesive layer from the carrier wafer and
cleaning any residual adhesive from the product wafer. The
cleaning process should be carefully controlled to avoid
damage to the dies or product wafer.
Direct placement D2W hybrid bonding
D i r e c t d i e p l a c e m e n t D 2 W h y b r i d b o n d i n g
Table 1: Comparison between W2W and D2W hybrid bonding according to main
decision criteria. involves picking and placing a die onto a target wafer,
followed by annealing to covalently bond the dies and
Collective D2W bonding process electrically connect them [4]. The first step in this
Collective D2W bonding involves the bonding of multiple process is selecting a suitable die carrier, as shown in
dies onto a wafer substrate in a highly accurate and reliable Figure 3. Depending on the requirements of the application,
manner. The collective D2W bonding process typically the carrier can be a film frame or a specially-designed and
consists of several key steps, shown in Figure 2, including fabricated die carrier. The selection of the carrier should be
carrier preparation with adhesive, die protection while based on factors such as die size, die thickness, and the number
handling, die population using a high accuracy D2W bonder, of dies to be bonded.
W2W die transfer of the carrier wafer to the product wafer, The next step is the carrier picking, which can be done
and finally, debonding of the die carrier and cleaning [2,3]. from a completed singulated wafer or a reconstituted carrier
The first step in the process involves preparing the carrier consisting of different dies. Once the die has been picked, it
wafer with a suitable adhesive material. The adhesive layer is necessary to activate and clean the surface before bonding.
should be uniform and have a sufficient thickness to provide Plasma activation is used to remove any contaminants and
adequate bonding strength. The carrier wafer should also be rehydrate the surface of the die, ensuring good bonding. The
compatible with the adhesive and should have a surface that plasma activation process is critical to ensure strong bonding
can be easily cleaned and prepared for bonding. between the die and the wafer.
In the next step, the dies are protected while being A high-accuracy pick-and-place process is essential for
handled to prevent damage or contamination. This may ensuring a high alignment accuracy with less than 200nm
involve the use of specialized handling equipment or on opposite corners of the die. This high-accuracy pick-
techniques, such as vacuum or tweezers. The dies should be and-place process is achieved using advanced equipment
handled with care to avoid any potential damage, which can and technologies. The controlled bond wave is initiated by
result in yield loss and reduced device performance. contacting the die center, ensuring a stable and uniform bond
Once the dies are protected, they are populated onto between the die and the wafer.
the carrier wafer using a high-accuracy D2W bonder.

Figure 2: Collective D2W hybrid bonding process flow.

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