Glass Solutions for Wafer Level Packaging

Glass substrates with fine-pitch through-glass via (TGV) technology give an attractive approach to wafer level integration. Glass can be made in very thin sheets (<; 100 um thick) which aids in integration and eliminates the need for back-grinding operations. Electrical and physical properties of glass have many attractive attributes such as the ability to provide low loss performance, adjust thermal expansion properties and low roughness with excellent flatness to achieve fine L/S. Furthermore, glass can be fabricated in panel format to reduce manufacturing costs. The biggest challenge to adopting glass as a packaging substrate has been the existence of gaps in the supply chain, caused primarily by the difficulty in handling large, thin glass substrates using standard automation and processing equipment. This paper presents a temporary bonding technology that allows the thin glass substrates to be processed in a semiconductor fab environment without the need to modify existing equipment. The approach utilizes a thin inorganic adhesion layer to bond a thin glass wafer to a silicon or glass handle wafer (Si handle wafer is the primary approach). The thin glass substrate, which may contain through-glass vias (TGVs), is then processed through downstream steps such as via fill, CMP, RDL/passive deposition, lithography and bumping. The bond is stable (remains temporary and without outgassing) to over 400 °C. Utilizing a Si handle wafer allows the thin glass to be processed leveraging existing processes, with only a mechanical de-bond to yield finished substrates. An attractive benefit to this approach is that it lends itself to creating wafer-level multi-layer stacks. We will provide an overview of the technology and examples of the demonstrated process.