Through Glass Via (TGV) Etching on Glass Core Substrates for High Density 3D Advanced Packaging Applications

The demands for increased data transmission rates and bandwidth as well as reduced signal loss are increasing while package size is getting bigger. To accommodate increasing package size and manage high frequency loss and warpage management, Glass substrates in advanced packaging are gaining momentum for heterogeneous integration of advanced semiconductor packaging. Based on Yole report in 2020, a 2.5-3 fold increase from 2019 to 2025 for the glass substrates is predicted. Glass core and Glass interposer could become a leading processing technology in advanced Panel Level Packaging (PLP). Cost effectiveness and high-frequency  characteristics of glass laid strong pathways for Advanced Packaging Roadmaps. However, insertion of glass poses several challenges such as CD uniformity of Through Glass Via (TGV) etch over different aspect ratio of via sizes.   Also due to the CTE mismatch between glass and metal, adhesion and stress management appears to be a huge issue for integration of TGV metallization and RDL layers.  This paper presents the detail of TGV etch process with respect to different glass types, laser modification methods, and aspect ratio.  Etching characterization over bath life as well as   with various Design of Experiments (DOE) was performed to address the HVM challenges.  Fabrication of TGV and metallization requires a good buffer layer (BL) on glass vias followed by Eless Cu deposition. Based on the types and properties of buffer layer, buffer layer serves the purpose of adhesion promotion liner (APL) as well as stress buffer layer (SBL).  Additionally, Electrode less (Eless) Cu would be beneficial to provide as seed layer for conformal or full TGV metallization.  Hence, a closer look into the development of Through Glass Via (TGV) processing, Adhesion promotion layer (APL), and Eless Cu techniques are discussed in this paper. A Wet process system has been developed to enable the TGV processing, Adhesion promotion, and Eless Cu for different types of glass substrates. Cross sectional and chemical analyses were done to validate the studies and the data were used to develop the glass etching, APL/SBL, and Eless Cu. Simulation and experimental data indicates that this approach is feasible to address glass processing and stress management challenges.