Study of EUV mask defect repair using FIB method

At the Photomask Japan 2010, we reported on the cleaning process durability and the EUV light shielding capability of FIB-and EB-CVD film based on carbon, tungsten and silicon containing precursors. The results were that the tungsten based FIB-CVD film showed no loss of film thickness after dry cleaning process, and the calculation showed that 56nm thick was sufficient for repairing clear defects on EUV mask with 51nm thick of absorber layer. On the other hand, carbon based FIB-CVD film suffered considerable loss in its film thickness and needed more than 180nm thick even if the 10nm thick of buffer layer between the CVD films and the capping layer supported the EUV light shield. In this paper, we will report on a newly developed repair method of clear defects on EUV mask using an FIB technique. The clear defects were repaired by removing or damaging the reflective ML (multi layer) underlying the clear defect area instead of applying the conventional FIB-CVD (Focused Ion Beam-Chemical Vapor Deposition) films. After removing the ML, the cross sectional pattern angle was approximately 83 degree and the sidewalls were covered with 15nm thick of Si and Mo mixing layer caused by Ga ions exposure. The performance of defect repair was evaluated by SFET (Small Field Exposure Tool) printability test. The exposure results showed that the ML etched area behaved as low reflection area and the printed CDs were proportional to the mask opening CDs. The study also revealed that the ML etched pattern was not sensitive to 50nm of focus error.