Near the end of device processing, aluminium metal is evaporated onto the patterned wafer to form electrical
contacts to the devices.
Evaporation is carried out using Physical Vapor Deposition (PVD). A small piece of aluminum
is placed in a resistively heated basket. When it is hot enough, atoms evaporate and float to the chip surface.
Vacuum is required so that nothing gets in the aluminum atoms’ way and so that they do not react with air to
form Al2O3.
