Essential Guide to Semiconductors, The

Laser Surgery: Etching Away the Transistors

Once the wafer is coated with photoresist, it's light sensitive and must be kept in the dark so that it doesn't accidentally get “developed” before it's ready. Fortunately for us, the photoresist is sensitive to light we can't see, so there's no need to shut off the lights in the clean room. The wafer still needs to be handled carefully, however, to avoid scratching its delicate and carefully prepared surface.

To develop the wafer, we put it into a machine called a stepper. Usually a robot arm takes a wafer off the top of a stack and places it in the stepper automatically. Mounted just a few inches above the wafer is a copy of the film negative that the chip designers created (which was described in ...