Hybrid bonding

www.3dic.org/Hybrid bonding

Hybrid bonding or metal/dielectric hybrid bonding is a direct bonding technology which obtains metal-metal bonding and dielectric-dielectric bonding simultaneously.

Cu/SiO2 Hybrid Bonding

Direct Bond Interconnect (DBI®)

See main article DBI

The DBI is a low-temperature bonding technology for Cu/SiO2 hybrid bonding, in which the SiO2-SiO2 bonding was formed after plasma activaiton, following by Cu-Cu bonding by post-bonding annealing. The annealing temperature is determined by the CTE of Cu and DBI pad thickness.

Cu/SiO2 Hybrid Bonding after Modified CMP

Combined SAB for Cu/SiO2 Hybrid Bonding

Cu/Adhesive Hybrid Bonding

• Ahdeisve-first Hybrid Bonding

One major challenge of low-temperature Cu/adhesive hybrid bonding is the bonding temperature mismatch between Cu-Cu and adhesives. Typically, the temperature required for Cu Cu bonding (350–400 ◦ C) is much higher than that of adhesive bonding/curing (≤250 °C, depending on the glass transition temperature Tg of the adhesives). Because the high Cu-Cu bonding temperature may damage the adhesive if it is not fully cured beforehand, it is difficult to obtain both Cu-Cu and adhesive bonding at the same temperature. Existing researches on Cu/adhesive hybrid bonding are typically conducted through an “adhesive-first” bonding approach, in which partially cured adhesive is thermo-compression bonded and highly cured in the first-step at a lower temperature (e.g., 250 ◦ C 1 h for benzocyclobutene, or BCB) before the second-step Cu Cu thermo-compression bonding at a higher temperature (350–400 °C). The “adhesive-first” hybrid bonding approach has issues such as large thermal stress and low throughput. Also, the mutual slip between the upper/lower substrates during the first-step adhesive bonding/curing may cause great misalignment of the final bonded structure.

• Cu-first Hybrid Bonding

Through the “Cu-first” hybrid bonding approach, Cu-Cu bonding is done at a low temperature within a short time (e.g., ≤600 s) prior to the long-time adhesive curing (which can be then conducted in batch without compression). To enable the “Cu-first” hybrid bonding, it is of great essential to obtain the Cu-Cu bonding at a reduced temperature that is comparable to or even lower than the adhesive bonding/curing temperature, which is typically below 250 °C or even 200 °C.

Because of the effective Cu surface activation by the combined reduction effects of the H-containing HCOOH vapor treatment, the Cu-Cu bonding temperature can be lowered to 180–200◦C, which is matched to the bonding/curing temperatures of many adhesives.

Cu/Adhesive hybrid interface bonded at 180 °C.[1]

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  1. R. He, M. Fujino, M. Akaike, T. Sakai, S. Sakuyama, and T. Suga, “Combined surface activated bonding using H-containing HCOOH vapor treatment for Cu/Adhesive hybrid bonding at below 200 °C,” Applied Surface Science, vol. 414, pp. 163–170, Aug. 2017.