High-NA EUV lithography: pushing the limits

EUV technology with its state-of-the-art tool generation equipped with a Numerical Aperture (NA) of 0.33 and providing 13 nm resolution is on the brink of entering high volume manufacturing. Extending the roadmap down to a resolution of 8 nm requires a high-NA successor tool. ASML and ZEISS are jointly developing an EUV scanner system with an NA of 0.55 to enable the continuation of Moore's law throughout the next decade. In this paper we motivate the top-level requirements of this high-NA tool, deduce implications on system design and present how they are solved in the tool. In particular, we address implications of the high-NA leading to large mirror sizes, introduction of a central obscuration and an anamorphic lens design resulting in the transition from full to half field. A consequence of the high-NA is a reduced depth of focus which is dealt with by an improved focus control of the system. The aberration level of the high-NA tool will be significantly reduced w.r.t. the NA 0.33 tool generation. This is achieved by extreme aspheres accompanied by an advanced mirror manufacturing process with corrections down to atomic scale. To enable mirror manufacturing to this precision the limits of mirror metrology are pushed out by transferring the whole measurement process into vacuum. Finally, we will give an update on the current status of the high-NA tool development and the build-up of the necessary infrastructure.