NSR 2005 i 12 i-Line

A stepper is a projection lithography tool used to transfer patterned features from a photomask onto photoresist on a wafer. A stepper exposes one field at a time and moves the wafer between exposures so the pattern can be repeated across the wafer surface. i-Line steppers belong to the optical lithography class used for patterned layer definition in semiconductor fabrication.

A lithography stepper projects a reduced image of a mask pattern onto photoresist using an optical imaging system. The tool aligns the wafer to previously formed pattern levels, exposes a selected field, and then steps the wafer to the next position for another exposure. Stepper operation is part of the resist patterning sequence that enables later etch, implant, or deposition pattern transfer.

A stepper sits in the photolithography portion of the wafer process flow after resist coating and prebake and before development. The exposed resist pattern created by the stepper is then used in downstream pattern transfer steps such as etch or ion implantation. Repeated use of lithography tools across many layers allows successive device and interconnect patterns to be aligned to one another.

Optical steppers are used wherever patterned resist images are needed on semiconductor wafers. Typical applications include defining active regions, isolation areas, contact openings, metal interconnect features, and other repeating chip patterns. Such tools are also used in processes that require overlay of new patterns to structures already formed on earlier layers.