Influence of sputter effects on the resolution in X-ray mask repair

When Focused-Ion-Beam Milling is used for repairing opaque defects on X-ray masks, the specific sputter effects such as redeposition of the sputtered material and reflection of the primary ions influence the obtained resolution appreciably. This physical behaviour leads to edge angles smaller than 90 graduation and to a shift of the milled pattern as well as to a specific kind of "proximity effect". That means, the repair of a defect could generate new defects due to the redeposited material which have to be corrected again. Furthermore, the achievable aspect ratio which depends on the sputter yield is limited to approximately 5 for gold under practical conditions.