The aluminum layer is etched using a PAN etch solution. PAN stands for "Phosphoric - Acetic - Nitric." These are the three acids which are mixed togther to form the etch solution.
The following steps make up the PAN Etch process:
The acids which make up the PAN etch solution are mixed according to the following formula (by volume).
Water 2 parts Phosperic Acid 16 parts Acetic Acid 1 part Nitric Acid 1 part
After the pan etch solution is made the remaining amount of solution can be stored in this bottle.
If there is some Pan Etch solution in the Pan Etch bottle, use that before making more.
Pour the PAN etch solution into the glass containter marked "PAN Etch".
Heat the PAN etch solution to between 40 and 45 degrees C.
Immerse the wafer in the solution and agitate. You will begin to see metal bubble up and lift off the surface. Conutinue to agitate for one minute AFTER you no longer see metal moving away from the wafer surface.
Rinse the wafer with water, then blow it dry with nitrogen.
After it is dry, check under the microscope to make sure that all the necessary Aluminum has been removed to prevent shorting.