Progress in extreme ultraviolet mask repair using a focused ion beam

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The key challenge in extreme ultraviolet (EUV) mask defect repair is to avoid or limit the damage to the sensitive reflective multilayer (ML) stacks on the mask substrate and repair <55 nm mask defects. Our EUV mask design employs an oxide buffer layer between the ML and the absorber to protect the ML during repair. We have developed both opaque and clear EUV mask defect repair processes using focus ion beam (FIB) based gas-assisted etching (GAE) and ion-induced deposition. The process has been successfully demonstrated on our TiN baseline mask by 10× EUV print tests of 100 nm resist lines/spaces. More importantly we have assessed the current FIB tool performance capability and compared it with the general requirements for repairing the EUV mask for the 70 nm lithography node. The characterization includes minimum “effective” beam size, etch selectivity, and edge placement precision. We discussed the required improvements and future directions in repair tool research and development in order for the mask repair technology to keep pace with lithography scaling in future generations.