Investigation of the process for glass interposer

Through glass via (TGV) interposer fabrication processes are critical techniques in 3D-IC integration, providing the short interconnection among different stacked chips and substrate. Nowadays, silicon is a mature material in semiconductor technology, but glass, a dielectric material, provides an attractive option due to its intrinsic characteristics for the advantages of electrical isolation, better RF performance, flexibility with CTE and most importantly low cost solution. In this investigation, the glass interposer by using TSV industry equipment and tooling was evaluated and developed and there are many challenges for processing. For process, the major differences between Glass and Si interposer are method for via formation and isolation. The test vehicle for Glass interposer is successfully processed. Glass material is composed with SiOx, it is good isolation for electrical current. The polymer-based PBO is used for passivation. For structure of glass interposer, there is one RDL on the front-side and backside, respectively. The other structure is 2 RDL on the front-side and one RDL one the backside. The CD of through glass via is 30 μm, it is formed by Corning Co. Cu overburden and Ti barrier are removed by wet etching process. For top RDL (line-width = 20μm), Cu plating process with seed layer (Ti/Cu) wet-etching process is applied. The PBO material is used for passivation, the process temperature is blow 200°C. Top UBM (15μm in diameter; 4μm/5μm-thick Cu/Sn) is formed with a top passivation opening (15μm). The structure is analyzed and demonstrated by SEM analysis. All the results indicate that the glass interposer with polymer passivation can be preceded and the cost for process is cheaper than Si interposer.