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 for semiconductor volume production. We refer 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 topography of resist patterns (critical dimension (CD), height, sidewall angle) and FEM's exposure conditions. Step 2: measuring the topography of resist patterns on a production wafers and feeding the topography 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 topography of the FEM with an optical CD measurement tool. Using the topography data, we obtained the following results. Focus: 27.0 nm (5.2 nm) and Dose: 1.8% (1.4 nm). The numerical value in a parenthesis shows the value of the estimated accuracy with changing CD. We also show other experimental results and some simulation results in this paper.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2005-07-15

Focus and Dose Measurement Method in Volume Production

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