Publication: Evaluating cu-to-cu direct bonding in ambient environment via surface treatment techniques
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Date
2025-09-01
Authors
Leow, Yen Houng
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Abstract
In semiconductor industry, the packaging trend and technology advance rapidly to
accommodate smaller and compact designs of electronic devices. Cu-to-Cu bonding
emerges as future of interconnect joints with its faster signal transfer with lower joint
resistance and better thermal dissipation, replacing conventional solder joints. This
research studies the effect of dry and wet etching as well as combination of both in
enhancing Cu-to-Cu direct bonding at ambient environment. Different temperatures of
260℃, 300℃ and 350℃ were being evaluated and compared, with low bonding
temperature (<300℃) is desired. Surface treatments with argon plasma for surface
activation and hydrochloric acid (HCl) for surface cleaning and smoothening were
assessed on Cu surface. The combination of both methods in different sequences were
also assessed and compared for their effects in bonding efficiency. Before bonding,
several analyses were conducted on Cu surface such as FE-SEM morphology inspection,
AFM surface roughness measurement, EDS elemental composition analysis and water
contact angle measurement. Subsequently, the Cu samples were subjected to
thermocompression bonding (TCB), with applied heat and pressure. After that, shear
test and Cu bonding interface inspection at cross-sectional view were included as post
bonding characterization. The correlation between Cu surface conditions towards
bonding strength at different temperatures will be discussed. In summary, surface
analyses showed that HCl acid is effective in smoothening and cleaning surface oxide,
while plasma could increase surface energy and remove carbon contamination. In terms
of bonding strength at 260℃, individual treatment of HCl acid gives best result up to
14.31MPa, showing the importance of clean and smooth Cu surface in TCB. On the
other hand, combination of methods might pose disruptions to their treatment effects.