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The Aerial Image Measurement Tool (AIMS) can estimate the wafer printability without exposure to wafer by using
scanner. Since measured aerial images are similar with wafer prints, using AIMS becomes normal for verifying issue
points of a mask. Also because mask design rule continues to shrink, defects and CD uniformity are at issues as factors
decreasing mask yield. Occurred defects on a mask are removed by existing mask repair techniques such as
nanomachining, electron beam and focused ion beam. But damages and contaminants by chemical and physical action
are found on the mask surface and contaminants above special size lead to defects on a wafer. So cleaning has been
necessary after repair process and detergency has been important. Before AIMS measurement, cleaning is done to make
same condition with shipped mask, which method brings repeated process - repair and cleaning - if aerial image was
not usual.
So cleaning effect after the FIB repair is tested by using the AIMS to find the optimized process minimizing the
repeated process and to get similar scanner results. First, programmed defect mask that includes various defect size and
type is manufactured on some kinds of patterns in DRAM device and sub-80nm tech. Next the defects on the
programmed mask are repaired by FIB repair machine. And aerial images are compared after the chemical cleaning,
non-chemical cleaning and without cleaning.
Finally, approximate aerial images to scanner results are taken regardless of cleaning process. It means that residue
originated from repair process doesn't affect aerial images and flexible process is possible between AIMS, repair and
cleaning process. But as the effect of minute particles and contaminations will be increased if pattern size is much
smaller, it needs to reconfirm the effect below the sub-60nm in DRAM device.
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