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10 May 2005 Focus and dose measurement method in volume production
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We propose a new inspection method of in-line focus and dose control at semiconductor volume production. We have been referred to this method as Focus & Dose Line Navigator (FDLN). Using FDLN, the deviations from the optimum focus and exposure dose can be obtained by measuring the topography of resist pattern on a process wafer that was made with single exposure condition. Generally speaking, FDLN belongs to the technology of solving the inverse problem as scatterometry. The FDLN sequence involves following two steps. Step 1: creating a focus exposure matrix (FEM) using test wafer for building the library as supervised data. The library means relational equation between the topography of resist patterns (critical dimension (CD), height, side wall angle) and FEM's exposure conditions. Step 2: measuring the topography of resist patterns on production wafers and feeding the topography data into the library to extrapolates focus and dose. To estimate the accuracy of FDLN, we had some experiment. We made a FEM with ArF lithography tool and measured the topography of the FEM with optical CD measurement tool. By using the topography data, we obtained following result as accuracy of FDLN. Focus: 27.0nm (5.2nm) and Dose: 1.8% (1.4nm). The numerical value in a parenthesis shows the value of estimated accuracy into change of CD value. We also show other experimental results and some simulation result in this paper.
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Hideki Ina, Satoru Oishi, and Koichi Sentoku "Focus and dose measurement method in volume production", Proc. SPIE 5752, Metrology, Inspection, and Process Control for Microlithography XIX, (10 May 2005);


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