Extreme Ultraviolet Lithography

This book describes the principles and basic technologies of extreme ultraviolet lithography (EUVL). The topics include why research on EUVL was begun and why an exposure wavelength of 13.5 nm was selected; the design of the optical system, which employs reflective mirror; the use of a multilayer film to make a reflective-type mask and how masks are inspected; an historical overview of the development of light sources; resist materials; and the recent performance of lithographic tools for mass production. Three innovations were key to the development: of Mo/Si multilayer films with a high reflectivity and to the shaping and metrology of aspherical mirrors with a precision of less than 0.1 nm. The technology for measuring figure error and the fabrication technology now meet the performance targets. Thus, EUVL has become the most practical lithographic technology for device fabrication at the less than 7-nm node.