MULTILAYER MIRROR TECHNOLOGY FOR SOFT-X-RAY PROJECTION LITHOGRAPHY

Recent advances in multilayer mirror technology meet many of the strin gent demands of soft-x-ray projection lithography (SXPL). The maximum normal-incidence reflectivity achieved to date is 66% for Mo/Si multil ayers at a soft-x-ray wavelength of 13.4 nm, which is sufficient to sa tisfy the x-ray throughput requirements of SXPL. These high-performanc e coatings can be deposited on figured optics with layer thickness con trol of approximately 0.5%. Uniform multilayer coatings are required f or SXPL imaging optics, for which maintaining the surface figure is cr itical to achieving diffraction-limited performance. In contrast the c oatings on the condenser optics will be graded to accommodate a large range of angles of incidence. Graded multilayer coatings can also be u sed to modify the figure of optical substrates without increasing the surface roughness. This offers a potential method for precise fabricat ion of aspheric imaging optics.