Photoresist

Absorbance: a decrease in absorption of the photoresist after
it has been exposed is called “bleaching”
.
Bleaching can provide a
more uniform exposure
because as the top layers
of the resist are exposed,
they become partially
transparent, allowing a
fuller exposure of the
lower layers.
Figure 8.13 Total absorbance of a layer of SPR511-A resist
before and after exposure. The difference between the two
curves is the actinic absorbance (courtesy Shipley).