Research on depth measurement of optically transparent glass via using nondestructive technology

Glass Via technology plays a crucial role in advanced electronic packaging, facilitating high-density electrical interconnections through glass substrates, which are increasingly considered a key technology for next-generation three-dimensional integration. Therefore, an accurate and efficient measurement method to control and inspect in process is essential. Specifically, the Blind Glass Via (BGV) depth is the key factor to guarantee high yield of the final product. In this paper, we propose a novel approach to enhance our homemade setup by integrating NIR spectral coherence interferometry technology, resulting in a significant amplification of interference signals on rough samples. Regarding the optical configuration of the integrated system, the operating spectral band and the illumination spectral band were designed to match the specific measurement positions. In addition, a dichroic beamsplitter was employed to enable efficient integration of the two spectral bands within a single optical system by realizing a shared optical path. Furthermore, for the depth measurement algorithm, a Gaussian interpolation-based Fourier transform peak extraction analysis method was designed to achieve high-speed and high-precision depth measurements. In this report, BGV with nominal CD 55 μm, and aspect ratio up to 5 was measured. Metrology results indicate the proposed system provides excellent correlation to SEM results.