January 1, 2013
Step and Repeat Technology
Rudolph steppers use projection optics to expose circuit patterns from a mask or reticle onto a substrate to achieve images with the optimal fidelity required for advanced packaging technologies. These systems employ light from a mercury arc lamp that is transmitted through a mask or reticle containing display circuit patterns. Substrates are aligned on the system and the mask is imaged through a projection lens in photoresist material coated on the substrate. The substrate is then moved, or "stepped", to a second position to expose an adjacent area. Images can be “stitched” together precisely to form larger circuit patterns without any noticeable change in circuit performance. The system repeats the step and exposure process until the entire substrate is patterned. Once the exposure process is complete, the substrate is developed with an alkali solution, such as TMAH or sodium hydroxide (NaOH), to reveal the underlying material. The imaged photoresist serves as a barrier that allows for processing the underlying metal or insulating layers. The substrates then continue through the etching, stripping, and deposition processes until multi-layer circuits are completed.