Exposure of binary masks using ArF (193nm) photolithography processing is a common practice for layers with less critical imaging requirements, but they may experience obstacles for high volume manufacturing; mainly defectivity or requalification cost concerns. The usage of chrome on glass (COG) mask types under ArF wavelength exposure has been shown to lead to chrome migration issues, impacting mask integrity and critical dimensions (CDs) on wafer. While not experiencing the same defectivity concerns as COG, using opaque MoSi on glass (OMOG) as a replacement greatly increases the cost to build the mask but reduces the requalification efforts. We have observed that attenuated phase shift masks (PSMs) built for KrF wavelength (248nm) exposure show the same functional performance as a binary mask under ArF exposure for 45nm node technology. Initial feasibility investigation involved simulating wafer exposure with an OMOG mask and a KrF PSM mask under the same conditions. To demonstrate wafer performance, masks with and without 2nd level processing were built to verify exposure and tool handling capabilities. The application of KrF PSM as a binary mask under ArF photolithography processing for less critical layers of mature technology nodes shows to maintain pattern integrity at a lower total lifetime cost, compared to COG or OMOG, while providing comparable results on wafer.
With each technology node, overall focus budgets have become increasingly tighter in order to meet the necessary product requirements. The 7nm node has required us to define new opportunities for addressing top contributors to the focus budget. Field curvature in particular has been identified as a key contributor to the intrafield focus budget, contributing around 50%. This paper will introduce two new methodologies for improving field curvature; one a hardware solution and one a software solution.
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