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.
The resist effect may have a significant impact on source mask optimization (SMO), because the CD change in response to dose, defocus and mask size variations can be substantially modified by the resist effect. In this paper, we elaborate on how the resist effect, represented by compact resist models, changes the cost function of SMO and affects the optimized source shapes and the corresponding lithographic performance. Based on the results, we present the guidelines of using compact resist models in SMO, especially for the case of the negative tone development (NTD) process.
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