8 Direct Cu to Cu Bonding and Alternative Bonding Techniques …
225
8.9 Cu–Cu Bonding—Equipment Landscape and State
of the Art
In terms of high-volume manufacturing (HVM) there is a limited number of 300 mm
WoW bonding equipment, while the supply chain grows more with CoW and definitely further for CoC thermo-compression bonding (TCB) equipment. Key equipment suppliers for 300 mm wafer-level Cu–Cu bonding equipment suppliers are:
EVG (Austria) and Suss Microtech (Germany). Mitsubishi Heavy Industries Group
(Japan) developed standard SAB equipment and Bondtech (Japan) developed and
integrated SAB equipment with plasma cleaning/activation, alignment and prebonding, bonding and heating chambers, both for 300 mm wafer bonding. For CoC or
CoW, a number of flip chip bonder equipment suppliers have adopted prior toolsets
or designed new TCB tools to accommodate faster heat ramp times, improved alignment and handling of multiple input materials (wafers, substrates/sub-panels/strips
in metal carriers or trays. Key TCB bonder suppliers/toolsets are: Toray (Japan),
ASM (Singapore), BeSi/Datacon (Austria) and K&S (USA), however this is not a
comprehensive list. In terms of applications and commercialization, surface activated
bonding (SAB) has been applied in volume production in metal laminates, MEMS
packaging, and OELD devices to ensure hermetic sealing against permeation of water
and oxygen from the atmosphere into these devices. Cu/SiO 2 hybrid bonding (DBI
® )
has been applied by Sony for 3D stacked back-illuminated image sensors (IMX260
used in Samsung Galaxy S7 Edge) [9], while new applications have been reported for
hybrid bonding for 3D stacked hybrid pixel detectors for X-rays at Fermilab [80–82].
8.10 Chapter Summary and Recommendations for Future
Research
In this chapter, we reviewed various Cu–Cu bonding methods and fundamental
material and surface characteristics aspects of bonding mechanisms. The effects of
Cu surface activation, diffusion, microstructure and surface passivation by capping
layers (e.g. metal, passivation and SAM’s) were discussed. Surface activation is of
great importance in obtaining seamless Cu–Cu bonding at below 250 °C or even at
room temperature. Cu/dielectric hybrid bonding using DBI
® , CMP and combined
SAB methods was also discussed. We introduced insertion bonding for Cu-TSV’s
leveraging high compression due to the “Cu nail-in-cavity” shape and configuration
resulting in Cu plastic deformation and seamless bonding. Equipment for Cu–Cu
bonding for HVM has been briefly introduced. Scaling to large surface area chips,
wafers or panels with higher warpage and high-density interconnects remains a challenge especially in meeting lower compression pressure, lower process times and
thermal requirements. In the near term, for higher Cu–Cu bonding adoption, more
effort is needed to drive lower process times, seamless bonding quality and reliability
225
8.9 Cu–Cu Bonding—Equipment Landscape and State
of the Art
In terms of high-volume manufacturing (HVM) there is a limited number of 300 mm
WoW bonding equipment, while the supply chain grows more with CoW and definitely further for CoC thermo-compression bonding (TCB) equipment. Key equipment suppliers for 300 mm wafer-level Cu–Cu bonding equipment suppliers are:
EVG (Austria) and Suss Microtech (Germany). Mitsubishi Heavy Industries Group
(Japan) developed standard SAB equipment and Bondtech (Japan) developed and
integrated SAB equipment with plasma cleaning/activation, alignment and prebonding, bonding and heating chambers, both for 300 mm wafer bonding. For CoC or
CoW, a number of flip chip bonder equipment suppliers have adopted prior toolsets
or designed new TCB tools to accommodate faster heat ramp times, improved alignment and handling of multiple input materials (wafers, substrates/sub-panels/strips
in metal carriers or trays. Key TCB bonder suppliers/toolsets are: Toray (Japan),
ASM (Singapore), BeSi/Datacon (Austria) and K&S (USA), however this is not a
comprehensive list. In terms of applications and commercialization, surface activated
bonding (SAB) has been applied in volume production in metal laminates, MEMS
packaging, and OELD devices to ensure hermetic sealing against permeation of water
and oxygen from the atmosphere into these devices. Cu/SiO 2 hybrid bonding (DBI
® )
has been applied by Sony for 3D stacked back-illuminated image sensors (IMX260
used in Samsung Galaxy S7 Edge) [9], while new applications have been reported for
hybrid bonding for 3D stacked hybrid pixel detectors for X-rays at Fermilab [80–82].
8.10 Chapter Summary and Recommendations for Future
Research
In this chapter, we reviewed various Cu–Cu bonding methods and fundamental
material and surface characteristics aspects of bonding mechanisms. The effects of
Cu surface activation, diffusion, microstructure and surface passivation by capping
layers (e.g. metal, passivation and SAM’s) were discussed. Surface activation is of
great importance in obtaining seamless Cu–Cu bonding at below 250 °C or even at
room temperature. Cu/dielectric hybrid bonding using DBI
® , CMP and combined
SAB methods was also discussed. We introduced insertion bonding for Cu-TSV’s
leveraging high compression due to the “Cu nail-in-cavity” shape and configuration
resulting in Cu plastic deformation and seamless bonding. Equipment for Cu–Cu
bonding for HVM has been briefly introduced. Scaling to large surface area chips,
wafers or panels with higher warpage and high-density interconnects remains a challenge especially in meeting lower compression pressure, lower process times and
thermal requirements. In the near term, for higher Cu–Cu bonding adoption, more
effort is needed to drive lower process times, seamless bonding quality and reliability