FABRICATION OF HIGH-RESOLUTION MULTILAYER REFLECTION ZONE PLATE MICROLENSES FOR THE SOFT-X-RAY RANGE

The fabrication of linear, circular, and elliptical reflective zone plate lenses by a multistep process using microfabrication technologies is reported. The diffractive elements were generated by electron-beam lithography on a Mo/C multilayer mirror obtained by means of the triode sputtering technique. The patterns were transferred anisotropically into the multilayer mirror by reactive ion etching in a fluorinated plasma. An intermediate metallic mask made by the lift-off process was used for the transfer process. The groove depth could be monitored by following the reflectivity of the structure with a helium-neon laser during etching. Linear, circular (with 0.4-mu-m outer zones), and elliptical Fresnel zone plates (with 0.8-mu-m outer zones) were produced. Test patterns with a 50-nm top and 90-nm bottom resolution were produced. The groove profile and dimensional control were also investigated.