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Until recently, opaque defects on photomask have been removed by laser evaporation. However there are several disadvantages in this repair technique. First an operator must visually align the laser irradiation spot and pattern edge, so high repair accuracy can not be obtained. Also when the area to be repaired is large the laser sputters the surrounding surfaces and the evaporation tends to redeposit on pattern edges causing them to swell thus increasing the probability of detection by inspection equipment. Additionally the laser repair technique has proven to be very difficult if the pattern defect is any complex geometry. The repair using Focused Ion Beam (FIB) has been developed to solve some of these issues, however this method has not yet been applied to the production line because of degradation of transmission rate and the damage to the glass substrate. This paper reports the evaluation on the performance of the FIB repair using a newly developed gas assisted etching (GAE) technique and the status of using FIB with GAE in the production line. By using GAE, the degree of glass damage has been reduced by a factor of ten as compared with the FIB repairs without GAE. A transmission rate of 94% (i-line) could be obtained on a conventional mask and 92% (i-line) on the Halftone Phase Shift mask (HT-PSM). Furthermore, by applying the post-treatment after the repair, the transmission rate of the repaired area could be recovered to the same level as the normal glass area. The printing characteristics for i-line of the GAE repaired in both conventional mask and HT-PSM has been also good, showing that the GAE FIB repair is applicable in the normal photolithographic process window and that this method can achieve the similar printing result in comparison with non- repaired area.
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