In order to mitigate phase defects on EUVL mask blanks, Fiducial Marks (FMs) should be located with high registration
accuracy by the EUV Actinic Blank Inspection tool, the E-Beam (EB) writer, and other inspection tools. The proposed registration accuracy is less than 10 nm for each tools . In our previous studies  and  we fabricated FMs by FIB etching, or resist exposure by the EB writer and etching process, and inspected those FMs by the EUV Actinic full-field mask Blank Inspection (ABI) prototype developed at MIRAI-Selete. The registration accuracy of those FMs with the MIRAI EUV ABI prototype were not enough due to a pixel size of 500 nm on the mask in order to achieve total less than 10 nm defect location accuracy on the EUVL mask blank. We studied the registration accuracy improvement of FM on the blank by the experiment with the MIRAI EUV ABI prototype to establish the phase defect mitigation method.
In this experiment, we took some images of FMs by moving the mask stage of the MIRAI EUV ABI prototype by lengths of sub-pixels. And we analyzed registration accuracy of FM by stringing those images shifting sub-pixel. This method can achieve less than 2.5 nm FM registration accuracy by the conditions equal to or more than 4 times quasimagnification, trench detection, and 50% threshold level In this presentation, we will explain the experiment results of FM registration accuracy improvement on the EUVL mask with MIRAI EUV ABI prototype to establish the phase defect mitigation method.