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Preliminary study on EPL mask repair technology for 45-nm node

Electron projection lithography (EPL) has high-resolution capability of meeting the 45-nm technology node, especially for the “hole” process. A first-generation EPL has been developed and improved at Nikon and Selete. Defect free mask is indispensable for successful introduction of this technology into the production stage. However, an EPL mask is considerably different from today's optical photomask, especially due to its 3-D structure. Hence the conventional methods of quality assurance used for optical photomask are not applicable for EPL mask. Selete is now developing a series of defect inspection and repair systems for an EPL stencil mask infrastructure. In our previous work we verified a number of defect inspection and repair systems through a sequential process. We confirmed good sensitivity for ”hole” inspection, and accuracy of consistent template repair method through the various hole-defect types. Based on our previous work, here in this work we focus on Gas Assisted Etching (GAE) because the majority of the defects are black type defects in smaller features, especially at 45-nm node. The motivation here is to investigate on GAE repair for real usage at 45-nm node. In this paper we verified the capability of repair technology for isolated holes including smaller features. Moreover, we confirmed that the problems encountered in dense hole forming can be resolved.