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Driven by the growth trend of portable electronic products, the integration of functions into smaller electronic components (semiconductors) becomes more important, such as advanced packing. The fan-out type is the fastest growing advanced packaging platform. Re-Distribution Layers (RDL) are mainly structures in which the wafer lines are redistributed. In the process of RDL the residual film thickness in nanometers after Chemical-Mechanical Planarization (CMP) step and the depth of RDL structure are mainly the parameters should be measured to ensure the yield rate. In this research, we demonstrate an optical system design of microscope type spectral reflectometry which is based on finite microscope system with reflective objective. The advantage of finite microscope system is less optical components, which leads to less UV and NIR attenuation for the purpose of thin film (~5 nm) and thick film (~100 μm) measurement. Adjustable illumination angle design is also included. The illumination light incident on the sample are designed as parallel as possible for increasing the reflective light rays from bottom of RDL. The spot size of measurement area is ~13 μm in diameter. Meanwhile, the corresponding algorithm including thin film interference model fitting and Discrete Fourier Transform (DFT) for high density RDL analysis are presented. Our non-destructive solution can measure thin film as thin as 5 nm and the depth of high density RDL with line width/ space = 1 μm/ 1μm. Metrology results from RDL structure and SiO2/Si standard reference material are presented.
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