Advanced Lithography

The chapter provides an overview of recent advances in lithography for the production of integrated circuits (ICs). In the first section of the chapter, a brief introduction about lithography basics such as image formation, image resolution in projection systems, and resolution enhancement techniques is provided. In the following section, advanced lithography based on ArF 193 nm deep-UV (DUV) sources is discussed thoroughly, including photoresist requirements and characteristics, plasma etching selectivity, and the multiple patterning techniques commonly adopted for resolution enhancement in these processes. After mentioning some non-optical lithographic methods such as electron beam lithography and nanoimprint lithography, which are mainly employed for mask fabrication or niche applications, a detailed discussion is dedicated to extreme ultraviolet lithography (EUVL), which represents the technology of choice for the future and promises to be able to support a further scaling of ICs’ critical size, as required by Moore’s law. In particular, the evolution of EUVL laser sources based on Sn plasmas over the years is described, and their role in the diffusion of the technology is discussed. The requirements of EUVL resist are also described along with the role of stochastics, which are especially relevant for this technology because of the lower number of photons involved in resist exposure compared to the former DUV technology. In the end of the chapter, the mechanisms related to EUVL resist development are analyzed, including energy deposition, acid generation, and polymer deprotection.