| Popis: |
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. |
