Essential Guide to Semiconductors, The

Etching Bath

Now that the entire wafer has been exposed with dozens of images of our little chip, it's time to use a little chemical wizardry to start cutting away the parts we don't want. If we bathe our wafer in a bath of just the right chemicals, all the soft parts of the photoresist (the parts that weren't exposed to light) will wash away, along with the insulating chemicals that were underneath. The hardened areas of photoresist, however, will protect the insulating material beneath them.

We've photographically carved away part of our layer cake, leaving tiny valleys in exactly the places we want. It's as if we'd taken a very sharp knife and carefully sliced away some parts of the chip, although no surgeon's scalpel is sharp enough (and ...