Photomask Developer: Photolithography is the process of transferring a pattern from a photomask onto the surface of a silicon wafer or substrate. The pattern is tranferred via an intermediate photosensitive polymer film called photoresist. Photolithography permits intricate details to be transferred to a substrate and allows multiple devices to be patterned at once. A pattern is laid out by a designer. This pattern is copied and repeated several times onto a photomask. Each group of replicated patterns normally make up a group called a die, which is seperated by regions called streets. The substrate that will receive the pattern is coated with either positive or negative photoresist (or simply resist), depending on the design. The photomask is aligned to the wafer, brought into contact with the wafer, and the photoresist is exposed to UV light. The wafer is placed in the developer solution which causes the pattern to appear in the photoresist film. Finally, the pattern is transferred to the underlying material (typically a silicon dioxide layer) by means of a wet or dry etching process.