EUV mask fabrication with Cr absorber

In an attempt to narrow the choice for an absorber used in EUV masks, different materials are being evaluated. These materials need to meet the absorber requirements of EW absorbance, emissivity, inspection, and repair, to name a few. We have fabricated masks using Cr absorbers. The absorber stack consists of a repair buffer of SiON and a conductive etch stop of Cr sandwiched between the SiON repair buffer film and the Mo/Si multilayer mirror deposited on a Si wafer. However, to increase the process latitude, the Cr etch stop needs to be removed from the stack, in particular for mask repair. The absorber layer was patterned using commercial DUV resist and the pattern was transferred using reactive ion etching (RIE) with halogen-based gases. Completed masks exhibited negligible shift in the centroid wavelength of reflectivity and less than 2 % loss in peak reflectivity due to mask patterning. Completed masks were exposed at Sandia National Laboratories' 10X EUV exposure system and equal lines and spaces down to 80 nm were successfully printed. The masks were also imaged in a microscope with 248 nm wavelength, and the focused ion beam repair selectivity to the buffer layer (SiON) was established. The paper summarizes the mask fabrication process, EUV printability, mask repair, inspection and emissivity for EUVL masks with Cr absorber.