Defect repair for soft x-ray projection lithography masks

The most promising option for masks intended for use in soft x-ray projection lithography (SXPL) at λ=13 nm is a reflective mask which uses a Mo/Si multilayer reflective coating. A variety of multilayer coated reflective mask technologies have been reported which can provide both high-resolution features and good reflectance contrast between the patterned and unpatterned regions. Repair of defects generated during patterning is a necessary feature of any practical mask technology. We have investigated the application of focused ion beam milling and deposition to programmed defects in the absorber layer of a SXPL Mo/Si multilayer reflection mask. Use of a sacrificial polymer barrier layer is described as well as milling and deposition conditions. The effect of ion implantation of the barrier layer on its removal after absorber repair is also reported. Both reflectivity measurements and resist images comparing repaired and unrepaired regions of masks are used to demonstrate the efficacy of the technique.