Abstract
For Extreme Ultra-violet Lithography (EUVL) targeting at 11nm and beyond design rules, the minimum printable
EUVL multilayer (ML) mask defect size can be as small as 20-25nm. As a result, the defect-free EUVL ML mask blank
fabrication remains the top challenge for EUVL mask. Aspects of this challenge include high quality blank substrate
material (low thermal expansion material) fabrication, substrate polishing, substrate cleaning, blank handling, ML
deposition, and high sensitivity substrate and blank defect inspection. High investment cost and potential low blank yield
due to stringent defect-free requirement can quickly drive up EUVL cost of ownership. It is anticipated, however, the
EUVL ML blank yield can be drastically improved if we can allow a few defects on a ML blank. Utilizing such a
"defective" grade mask blank to fabricate a defect-free EUVL mask requires several defect mitigation schemes during
mask patterning processes. These schemes include modifying mask absorber pattern via repair tool to compensate the
effect of an adjacent ML defect and using absorber pattern to cover the ML defects. In this paper, we focused on the
study and demonstration of using device pattern to cover limited number of blank defects. The steps of this defect
mitigation process include blank fiducial mark patterning, defect location relative to fiducial mark precision
measurement, automated pattern shift solution simulation for a given ML defect map, and precision alignment of the
device pattern to the blank defects during e-beam write. With these steps, we have successfully demonstrated the
coverage of several targeted ML blank defects simultaneously via global device pattern shift.
