Exploring the XUV projection lithography design space

At sub 5 nm wavelengths, XUV projection systems offer one potential path toward the next generation of lithography systems. Alternative paths such as hyper-NA EUV suffer from a smaller depth of focus, raising challenges for wafer alignment. XUV optics remedy this through a combination of a reduction in wavelength and a return to lower numerical aperture, allowing for higher depth of focus at an improved resolution. This work surveys the reflective design space for XUV projection optics by adapting current EUV finite conjugate relays to shorter wavelengths. Both classical aspheric and freeform designs are examined across a range of field sizes, magnifications, numerical apertures, and mirror counts. A custom CODE V macro is used to automatically generate clearance constraints for arbitrary complex folding geometries, saving time during the design process. These considerations establish a coherent structure for further development of XUV projection optics.