Specific Process Knowledge/Bonding/Eutectic bonding
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Eutectic Bonding
Eutectic bonding depends on a formation of an eutecticum in the bond interphase. This makes bonding of two substates by use of eg. a AuSi eutecticum possible at temperatures much lower than the actual melting points of either of the two (in this case bonding can be done at around 390oC). The bonding strecth is quite good, but far from as good as anodic bonding. Different eutecticums have a different eutectic (bonding) temperature.
| Eutecticum | Eutectic temperature | Bonding temperature in EVG NIL |
|---|---|---|
| AuSi | 365oC | 390oC |
| AuSn | <300oC | 300oC |
| AuSnNi | . | . |
Please be advised that it is notoriously difficult to use the EVG NIL bond aligner, due to its manual nature it is strongly advised to book extra time to do alignment. However alignment of ±2 microns is possible by very exprienced users. The alignment marks (on the masks) are to be positioned at y=0 and x=±40mm for 4", for optimal result. It is possible to use both backside alignment and IR alignment however IR alignmant is more accurate, since only one aligning is used. However it is very important to use dobbelt polished wafers to have enough IR light to see the patterns.
Bonding procedure
- Remember to use double side polished wafers for IR alingment.
- Align the wafers
- Place the chuck and graphite electrode in the chamber.
- Close the chamber.
- Turn the µm screw on top of the chamber to set the desired stack height.