Low Temperature Cu-Cu Bonding Using an Intermediate Sacrificial Sn Layer

Thermocompression Cu-Cu bonding needs both high temperatures ( 300 ^{\circ }\text {C}\sim 400 °C) for bonding and annealing and complicated chemical mechanical polishing (CMP) for surface pretreatment. This paper reports a new CMP- and annealing-free Cu-Cu bonding method that is initiated by a sacr...

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Bibliographic Details
Published in:IEEE electron device letters 2023-01, Vol.44 (1), p.116-119
Main Authors: Wang, Zilin, Shi, Yunfan, Wang, Zheyao
Format: Article
Language:English
Subjects:
Annealing
Bonding
Bonding strength
Chemical-mechanical polishing
Copper
Formic acid
High temperature
Intermetallic compounds
Low temperature
Metal compounds
Redox reactions
Resistance
Silicon
Surface pretreatments
Surface roughness
Surface treatment
Temperature measurement
Tin
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Summary:Thermocompression Cu-Cu bonding needs both high temperatures ( 300 ^{\circ }\text {C}\sim 400 °C) for bonding and annealing and complicated chemical mechanical polishing (CMP) for surface pretreatment. This paper reports a new CMP- and annealing-free Cu-Cu bonding method that is initiated by a sacrificial Sn layer. This method includes three steps. (1) A Cu-Sn bump is reflowed at 250 °C with redox gases to change the Sn layer from solid to porous by sequential redox reaction. (2) Pre-bonding is performed at 200 °C to change the porous Sn to porous Cu-Sn inter-metallic compounds (IMCs) at solid-state. (3) Final bonding is performed at 250 °C with formic acid gas sweeping to reduce and volatize the Sn from the IMCs, changing the Cu-Sn bonding to Cu-Cu bonding. Using this method, Cu bumps with a diameter of 5\,\mu \text{m} and a pitch of 25~\mu \text{m} have been successfully bonded with high bonding strength and high yield.
ISSN:0741-3106
1558-0563
DOI:10.1109/LED.2022.3221375