REFLECTIVE MASK TECHNOLOGIES AND IMAGING RESULTS IN SOFT-X-RAY PROJECTION LITHOGRAPHY

In this work we investigate and compare a variety of technologies for patterning high resolution Mo/Si multilayer reflective x-ray masks for use at wavelengths near 13 nm. The patterning methods investigated include: absorbing layers deposited on top of multilayer reflectors, reflective coating removal by reactive ion etching and ion damage of multilayer regions to form a planar mask structure. Large area samples were prepared by each of the above methods and reflectivity measurements made to determine the expected mask contrast. The reflectivity data are compared with simulation for the absorber overlayer and etched multilayer measurements. Our results indicate that reflectivity changes between 5 and 300 were effected. Fine patterning tests show that mask features as fine as 0.1-mu-m can be achieved in each technology. The advantages, process complexity, and limits of each method are discussed. We also report the first use of an x-ray reflectance mask to print 0.1-mu-m features in resist. The developed resist images obtained using reflection masks in a 20:1 Schwarzschild projection camera compare favorably with transmission mask results obtained using the same optical system.