For Chrome binary masks, FIB defect repair has become increasingly challenging as feature sizes and exposure wavelengths are reduced. Chrome opaque defects are typically the most difficult to remove due to the lack of a highly effective gas chemistry for enhancing the FIB removal process. Repair artifacts such as gallium staining from ion beam exposure, quartz damage and re-deposited material are all important factors to be considered. New processes continue to be developed to extend FIB mask repair to the 100nm lithography node using a 193nm exposure wavelength. FEI, under an International Sematech funded program has developed processes to target the following criteria: Edge Placement: 15nm, 3sigma Transmission: >95%, lambda=193nm Maximum Quartz Damage: <10nm before post processing Ideally, these specifications should be met simultaneously. However, in the case of quartz damage, it is of greater importance to consider the volume of damage after post-processing. Chrome opaque defects on previous generations of masks have typically been removed by a first step using a combination of etching gases which enable the removal of chrome and a second repair step which, in combination with a focused gallium ion beam, removes the gallium implanted quartz resulting from the initial chrome removal. The primary issue becomes a transmission loss mainly due to excessive quartz damage resulting from the gallium removal and also a trench (commonly referred to as "riverbed") that was created during the initial chrome removal step. An edge bias into the chrome line is commonly used to restore transmission at best focus, typically measured at the exposure wavelength on AIMS (Aerial Image Measurement System). However when repairs are evaluated against the emerging specification of AIMS through focus variation, it becomes apparent that it is more desirable to use a process that provides less CD variation through focus.
