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The design of microscope type spectral reflectometry for the depth measurement of high-aspect-ratio through silicon via

Through Silicon Via (TSV) interconnect technology have been used to serve a wide range of Three Dimensional Integrated Circuit (3D-IC) production for higher integration and higher frequency purposes. Therefore, the inspection of depth and Critical Dimension (CD) of TSV becomes a key issue for yield rate evaluation. In this research, we demonstrate an optical system design of microscope type spectral reflectometry which is based on finite microscope system. The advantage of finite microscope system is less optical components, which leads to less UV and NIR attenuation for the purpose of thin film (~50 nm) and thick film (~50 μm) measurement. The illumination light incident on the sample are designed as parallel as possible for increasing the reflective light rays from bottom of TSV. The spot size of measurement area is 30 μm in diameter. Meanwhile, the corresponding algorithm including thin film interference model fitting and Discrete Fourier Transform (DFT) for high aspect ratio TSV analysis are presented. The thickness of oxide film and the depth of TSV can be calculated simultaneously. Our non-destructive solution can measure TSV opening diameter as small as 5 μm and aspect ratio greater than 15:1. The measurement precision is in the range of 0.03 μm. We also evaluate the total measurement uncertainty which is around 0.22 μm. Metrology results from actual TSV wafers are presented. The SEM results were made as comparison.