Fabrication and analysis of extreme ultraviolet reflection masks with patterned W/C absorber bilayers

We report on a novel procedure developed for the fabrication of reflection masks for extreme ultraviolet lithography. The procedure involves the deposition and patterning of an absorber bilayer (40 nm W and 25 nm C) on Mo/Si multilayer blanks. The C layer is used to protect the underlying Mo/Si multilayer structure during processing and repair. The pattern is written with an e-beam pattern generator into EPR resist and is transferred into the absorber bilayer with three consecutive rf etching processes. We have investigated the effect of the full mask making procedure on the multilayer reflectivity using 13 nm radiation. The procedure causes some oxidation of the top Si layer of the multilayer, an effect which is confirmed by XPS measurements. However, the method does not affect the multilayer reflectivity to within narrow tolerances. The profiles of patterns in the absorber layer are inspected with a SEM, showing patterns with a feature size of 250 nm and side wall slope angles of 80 degrees. An indication is found that cleaning of the substrate with ion etching prior to the fabrication of the mask blanks reduces the defect density. (C) 1997 American Vacuum Society.