Fusion bonding

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Fusion bonding
Technology Details
Other Names Fusion Bonding, Direct Bonding
Technology Substrate bonding
Equipment List of fusion bonding equipment
Materials %Optional materials processed%

Fusion bonding forms an Si-Si bond and the interface between two highly polished, flat and clean substrates. Initial contact will form a bond that is then enhanced with an annealing step.


The LNF has two bonders available for fusion bonding.

SB-6E Bonder

Main article: SB-6E Bonder

This is the recommended tool for fusion bonding. The default setup on the SB-6E Bonder is for 4 inch round substrates. 6 inch round substrates can also be accommodated but a tooling change must coordinate with the tool engineer. Alignment for 4" and 6" round samples is accomplished using the MA-BA-6 Mask-Bond Aligner in Bond Alignment mode.

EVG 520IS Bonder

Main article: EVG 520IS

The EVG 520IS can easily be used to bond pieces, 4" and 6" wafers. Bond alignment for 4" and 6" wafers is done with the EVG 620 Bond Aligner.

Method of operation

Polished, clean substrates are brought into contact and a bond spontaneously forms. The bonded stack is then annealed at a higher temperature (>700°C) to remove either water or hydrogen gas and strengthen the bond.


Fusion wafer bonding is used to join multiple substrates together. It is frequently used at the end of process to join two substrates together for packaging. It is also used to create enclosed channels or chambers, and to make complicated 3D structures, or devices that are very high aspect ratio. Fusion bonding has the advantage of being able to bonding like materials together which removes the CTE (coefficient of thermal expansion issues) that can arise in other types of bonds.


Substrate Flatness

The bow should be <0.5um.

Substrate Smoothness

The bonding areas need to have an Ra of less than 40Å.


Fusion or direct bonds can be formed between the following Silicon based surfaces: Si:Si, SiO2:SiO2, Si:SiO2, SI:Thin Silicon Nitride (100-200nm), Thin Silicon Nitride: Thin Silicon Nitride. This technique can be used for bonding other materials if they are mirror smooth, flat and can be hydrated.


Madou, Marc J (2012), Fundamentals of Microfabrication and Nanotechnology, Volume III