ABSTRACT
Photolithography processes are used to define active and passive devices, as well as interconnect wiring between these on semiconducting wafers. In general lithographic processes are used for numerous patterning steps, including the following: create semiconducting regions by ion implantation, isolate devices from each other, remove material, and add conducting layers. Photolithographic processes are used to transfer an image from a reticle or mask to the wafer. In III-V processing, 10 to 15 lithographic steps are needed to complete integrated circuit (IC) fabrication. This may involve a few layers for active devices, for example, contacts and gates, a few more for thin-film resistors and interconnect layers, and a few more for backside processing. The cost and cycle time of the whole fabrication process depend upon the number of lithography steps. Photolithography plays a central role in IC fabrication. The nature of other process steps used in the overall fabrication varies a lot from step to step, for example, from ion implantation to plasma etching and technology type (high-electron-mobility transistor [HEMT] vs. heterojunction bipolar transistor [HBT]), but the photolithography part can be common. The photolithography process based on the use of masks or reticles will be discussed here in detail; however, creation of the pattern directly on the wafer will be discussed only briefly.
