Performance Comparison between Attenuated PSM and Opaque MoSi on Glass (OMOG) Mask in Sub-32nm Litho Process

During the development of optical lithography that has been extending to 32 nm and beyond, it is found that the selection of mask blank types has a very strong impact on minimum feature process window, or critical dimension performance that can be achieved, which will affect ultimate wafer lithographic performance. Although the industry-standard 6% attenuated phase shifting mask (PSM) with 67nm MoSi has been widely used, as the manufacturing design rule continues to shrink, it will introduce quite a few challenges, such as, defect inspections, imaging contrast, or NILS, and mask error enhancement factor (MEEF) [1]. Meanwhile, the standard chrome-on-glass mask, compared with 6% Att. PSM, is unable to support the minimum feature required in lithographic process windows and through pitch requirements. To alleviate this problem, a new type of binary mask with Opaque MoSi On glass (OMOG) is gradually accepted and used in 32 nm. In this paper, both 6% attenuated PSM and OMOG mask have been evaluated with 28 nm patterns. PSM and OMOG mask's critical dimension uniformities (CDU) are compared. Further more; we have also compared wafer line width roughness (LWR), After Development Inspection (ADI) CDU, MEEF, through pitch process window including Depth of Focus (DOF) and Exposure Latitude(EL). Our result shows that, for bright field and dark field mask, OMOG mask show different behavior than PSM mask in lithographic process performance. As above, whether OMOG can replace 6% attenuated PSM as 32 nm/28 nm main stream mask blank will depend on mask performance, litho performance, and device requirements.