The detailed patterns are created on the layers of the silicon dioxide using a century-old printing technique called photolithography. A thin layer
of light-sensitive polymer, called photoresist, is applied over the silicon dioxide. Ultraviolet light projected through a glass mask-so thin that "pin holes" a few atoms wide can render it unusable-print
each layer's circuit pattern on the photoresist.
The exposed photoresist is washed away in solvent baths, etching the protective oxide layer with the shape of the circuit patterns. Tiny holes are
then etched into the oxide layer in preparation for the next major process step.
