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4 April 2007 Focus and dose controls, and their application in lithography
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We have proposed a new inspection method of in-line focus and dose controls for semiconductor volume production. We referred to this method as the focus and dose line navigator (FDLN). Using FDLN, the deviations from the optimum focus and exposure dose can be obtained by measuring the topography of the resist pattern on a process wafer that was made under a single-exposure condition. Generally speaking, FDLN belongs to the technology of solving the inverse problem as scatterometry. The FDLN sequence involves following the two steps. Step 1:creating a focus exposure matrix (FEM) using a test wafer for building the model as supervised data. The model means the relational equation between the multi measurement results of resist patterns ( e.g. Critical dimension (CD), height, sidewall angle) and FEM's exposure conditions. Step 2: measuring the resist patterns on a production wafers and feeding the measurement data into the library to extrapolate focus and dose. To estimate the accuracy of FDLN, we performed some experiments. We developed a FEM with an ArF lithography tool and measured the resist patterns of the FEM wafer with the advanced CD-SEM (Critical Dimension-Scanning Electron Microscope). Using the MPPC (Multiple Parameters Profile Characterization) data from the advanced CD-SEM, we obtained the following results. Focus: 21.5 nm (4.1 nm) and Dose: 1.5% (2.0 nm). The numerical value in a parenthesis shows the value of the estimated accuracy with changing CD. We also show other experimental results in this paper and the application of the focus and dose controls for semiconductor exposure tool.
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Hideki Ina, Koichi Sentoku, Satoru Oishi, Tomoyuki Miyashita, and Takahiro Matsumoto "Focus and dose controls, and their application in lithography", Proc. SPIE 6518, Metrology, Inspection, and Process Control for Microlithography XXI, 651807 (4 April 2007); doi: 10.1117/12.710456;

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