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Figure 4: Schematic illustrations of: a) the bond strength measurement and delamination caused by nanoindentation; b) a Berkovich tip; and c) a Cube Corner tip.
vapor deposition [PECVD]) was used as the Generally, a Berkovich indenter is used to Corner tip also has a sharper shape than
bonding interface. After planarization of the measure mechanical characteristics with the Berkovich indenter (Figure 4b-c).
LT-SiO 2 , the top wafers were thinned down NI. Nevertheless, Cube Corner indenter It has been reported that the threshold
and singulated into a die. The die and wafer tips were used in this study because indentation failure load (i.e., the load at
surface are plasma activated by a standalone the bonding dielectrics are relatively which the material does not crack) for
plasma activation system that is compatible thin. The geometry of these indenters bulk materials decreases significantly as
with the wafer and dicing frame. The die is described by Morris, et al. [14]. The the sharpness of the Cube Corner’s tip
stacking was then carried out using a full- ideal Cube Corner has an axisymmetric increases, and the threshold indentation
auto die bonder compatible with D2W hybrid equivalent angle of 35.26° and that of the load for radical failure decreases
bonding. After bonding, the wafers were Berkovich indenter’s is 65.27°. The Cube significantly with hardness [15].
annealed in an N 2 atmosphere at various
temperatures for one hour. Figure 3a shows
the picture of the test sample right after
bonding. Both W2W and D2W samples were
observed for voids at the interfaces using a
scanning acoustic microscope (SAM) after
bonding and post-annealing.
Bond strength measurement methods.
The bond strength of W2W bonded pairs
is measured using the DCB method
in a glovebox (GB) with an anhydrous
environment and at ambient temperature
as a reference. More details of the
measurement condition can be found in
reference [13].
For the NI test, the bonding interface
needs to be revealed. For this purpose,
the bulk silicon of the top dies (or
wafers) was removed by back-grinding
and wet etching (Figure 3b). Instead
of using time-consuming techniques
such as GHz SAM or transmission
elect ron m icroscopy (T EM ), we
employed scanning probe microscopy
(SPM) images from the top surface
to calculate the delamination. The
obtained SPM image was analyzed, and
the delamination area was defined from
the image.
T he s che m at ic d r aw i ng of N I
equipment is shown in Figure 4a. The
Cube Corner indenter tip is used to
measure the interfacial bond strength.

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