Repair of natural EUV reticle defects

Abstract

Defects of the multi-layer (ML) mirror on a EUV reticle, so-called ML-defects, are a prime aspect why EUV mask defectivity is considered a challenge before EUV lithography can be used for the production of future node integrated circuits. The present paper addresses the possibility to mitigate the printability of these defects by repair. Repair of natural EUV mask defects is performed using the electron beam based Carl Zeiss MeRiT® repair technology and is evaluated by wafer printing on the ASML EUV Alpha Demo Tool (ADT) installed at IMEC. Both absorber defects and ML-defects are included. The success of absorber defect repair (both opaque and clear type) is illustrated. For compensation repair of ML-defects experimental proof of the technique is reported, with very encouraging results both for natural pits and bumps. In addition, simulation is used to investigate the limitations of such compensation repair, inspired by the residual printability found experimentally. As an example it was identified that alignment of the compensation repair shape with the ML-defect position requires sub-20nm accuracy. The integration of an Atomic Force Microscope (AFM) into the repair tool has been an important asset to cope with this.