Abstract

One of the many technology areas that lie on the critical-path to the success of soft X-ray projection lithography (SXPL) is the fabrication and metrology of aspheric mirrors. I will review the progress of our collaboration with a number of companies to determine if the mirror fabrication and metrology technologies can be developed so that SXPL can meet the early next century demand for 0.1 μm design rule devices. The figure and finish tolerances for these mirrors are well beyond the current state-of-the-art for aspheres and even beyond industry's capability to fabricate spheres. To achieve the desired imaging capability will require mirrors with subnanometer figure errors over the full spatial frequency bandwidth, from 10 nm to 250 mm. Although exact full bandwidth tolerances have not been determined, we have estimated that the nanoscale rms roughness (as measured over a bandwidth of 10 nm to 1.0 μm) must be less than 0.1 - 0.2 nm so that high reflectivity multilayers can be attained. Specifications for the figure errors of a 5X reduction system being developed by GCA/Tropel range from 1.0 to 3.0 nm PV (depending on the mirror) for a 36 term Zernike polynomial fit. Although we have not yet estimated the specification for spatial frequencies between 1.0 μm and 25 mm, there is evidence that they could have a significant effect on imaging performance at X-ray wavelengths near 14 nm.¹

© 1993 Optical Society of America