Closing the gap for EUV mask repair

Abstract

The EUV-photomask is used as mirror and no longer as transmissive device. In order to yield defect-free reticles, repair capability is required for defects in the absorber and for defects in the mirror. Defects can propagate between the EUV mask layers, which makes the detection and the repair complex or impossible if conventional methods are used. In this paper we give an overview of the different defect types. We discuss the EUV repair requirements including SEMinvisible multilayer defects, and demonstrate e-beam repair performance. The repairs are qualified by SEM, AFM and through-focus wafer prints. Furthermore a new repair strategy involving in-situ AFM is introduced. Successful repair is demonstrated on real defects.