Page 32 - Chip Scale Review_September-October_2023-digital

Self-assembly process and factors. Surface particles can create the hydrophilic bonding area and the
integration challenges bonding defects, whereas organic surrounding hydrophobic material. The
A second paper was presented at residuals lead to outgassing during results obtained are very good from the
IEEE ECTC 2023 [8] that described the thermal annealing. Pristine surfaces perspective of yield.
latest progress on bonding defectivity, are therefore required before bonding. S e c o n d , s t e p h e ig h t pl a y s a n
the role of step height and the challenges After reviewing several organic defects, important role in the self-assembly
of Cu integration. die preparation was carefully optimized process. Step creation is necessary for
First, bonding qualit y directly to ensure a high quality bonding water containment, with taller steps
i mpacts t he elect r ical y ield a nd interface with intact self-alignment correlated with better containment.
mechanical stabilit y of the D2W capabilities, which means maintaining In our previous work, the step height
assembly and can be affected by several a good surface-energy contrast between was set at 15µm, which produced
sufficient containment, but may be too
tall for full integration. Indeed, after
self assembly, other processes such as
the creation of through-silicon vias
(TSVs) or other routing or bonding
layers, may be needed. Those processes
are easier to integrate when die and
wafer surfaces have shallower steps.
LEADERS IN To optimize compatibility with these
future applications, we experimented
MICRO DISPENSING t o det e r m i ne t he m i n i mu m st e p
height compatible with successful
TECHNOLOGY self assembly. Investigation of a range
of step heights from 10µm to 0µm
revealed that step heights of 1µm or
SMALL REPEATABLE VOLUMES less are suitable for use with the self-
ARE A CHALLENGE, BUT NOT assembly technique. This smaller step
IMPOSSIBLE IF YOU HAVE BEEN size should facilitate the integration of
CREATING THEM AS LONG AS WE HAVE. any subsequent process steps required
to obtain the final product. The results
confirmed the need for both chemically-
induced WCA contrast and a physical
TO DO IT WELL, step to contain the water droplet and
ensure accurate self alignment.
WE PROVIDE THREE THINGS: Because self assembly involves
hybrid bonding, it is essential to
investigate the compatibility of this
process with Cu. The following two
Dispensing Expertise in a variety of microelectronic aspects were studied: 1) the impact of
packaging applications. the process steps photolithography,
etching and stripping, on the integrity
Feasibility Testing & Process Verification based of the Cu, and 2) how water affects
on years of product engineering, material flow testing the Cu. Among our major findings,
and software control. we demonstrated a proof-of-concept
integration of Cu pad fabrication
Product Development for patented valves, using the self-assembly process.
dispensing cartridges, needles, and accessories. Some nanotopography degradation
was obser ved on the Cu su r face
because of the stripping chemistry,
but no significant oxidation due to
contact with water was visible. These
results are encouraging, paving the
Our Micro Dispensing product line is proven and trusted by way toward the commercialization
manufacturers in semiconductor, electronics assembly, medical of self assembly in high-volu me
device and electro-mechanical assembly the world over. ma nufact u r i ng applicat ions. We
will now focus on improving the Cu
www.dltechnology.com.
nanotopography and the electrical
characterization of the process.
216 River Street, Haverhill, MA 01832 • P: 978.374.6451 • F: 978.372.4889 • info@dltechnology.com

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