Specific Process Knowledge/Bonding/Anodic bonding

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Anodic Bonding

Anodic bonding can only occur between a Silicon wafer and a Pyrex (Borofloat) glass, not a quartz (fused silica). It is a strong chemical bond made by an E-field depleting the surface of the Pyrex wafer from Na+ ions. Hence it is very important to stack the Si wafers and the Pyrex wafer in the right order. Otherwise the Pyrex wafer could bond to the chuck or electrode, depending on the direction of the E-Field. The Wafer Bonder 02 only operates with an negative voltage meaning that one should always place the Si wafer closest to the chuck, and the Pyrex wafer closest to the electrode. Almost no force is needed to push the wafers together normally 1000 mbar. For a normal bond the temperature used is 400°C and the voltage is 600V. It is possible to decrease the temperature if one increases the voltage, eg. T=320°C and V=1200V.

Try and put this as one of the last steps in you process sequence, since you cannot do high temperature steps in Nanolabs cleanroom with Pyrex wafer. This also includes the plasma systems.