With lithography, the design data is transferred to the wafer. To do this, the photoresist exposed to UV light and becomes soluble at these points for the developer.
In order not to expose the rest of the photoresist the entire clean room is only illuminated with yellow light without any UV component.
with an automatic coating machine a thin layer of photoresist applied on one side of the wafer. In addition it need several drying and steaming chambers for good photoresist adhesion.
The laser imagesetter writes the design data directly on the wafer surface. The beam comes with acousto-optical elements moved and modulated.
The development of the photoresist takes place in a puddle process. A compressed air bed protect the backside of the wafer from pollution.