Development of focused-ion-beam repair for quartz defects on alternating phase-shift masks

Alternating phase shift masks are being developed for below 0.20 micrometer lithography. Repairing shifter defects is one of key technologies to make them practical. Etched quartz shifter is mostly utilized for KrF excimer laser. Gas assisted etching (GAE) with a focused ion beam has been investigated for reducing Ga stain in repairing quartz defects. This method, however, has difficulties, occurrence of a 'riverbed' and another in end-point-detection, because a defect and the substrate are of the same material. This paper describes a new method of repairing quartz defects. It consists of two steps. In the first step, a defect is etched except the edge region by using GAE before wet etching. Therefore, the edge remains like a wall. In the second step, the edge wall is removed during wet etching. For evaluating the effectiveness of this method, a test plate containing two types of programmed defects, quartz extrusions into clear and quartz bridges, were prepared. After the repair, the printability of the repaired area was evaluated with AIMS simulation. Riverbeds were not observed after the repair and the critical dimension (CD) variation of the repaired area through focus change was within plus or minus 5% around 0.2 micrometer between defocus of plus or minus 0.5 micrometer for 0.2 micrometer lines and spaces. The practicability of our new method is also reported with respect to its allowance for side-wall thickness, that of etching depth and its dependence on defect size.