Thin Glass Substrates with Through-Glass Vias
Authors: Shorey Aric , Nelson Shelby , Levy David , Ballentine Paul 
Published: January 2025

Glass substrates with fine-pitch through-glass via (TGV) technology gives an attractive approach to wafer level packaging and systems 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 low RF loss, the ability to 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.

There have been a number of research articles published over the past several years showing the advantages that glass based solutions can bring to packaging and systems integration including RF front ends, interposers, MEMs devices, and integrated photonics. [1-10]. RF applications of glass in particular are gaining interest for use as a substrate for filters, switches, true time delay modules, and millimeter antenna arrays. The advantages include low insertion loss as the frequency increases above a few GHz relative to Si-based solutions and higher integration density compared to laminates and ceramics. Furthermore, numerous articles have shown the ability of glass to pass typical reliability testing including thermal shock and drop tests [e.g. 5, 8]. The challenge has been addressing how to make the transition from small scale demonstration to providing solutions that can transition into high volume manufacture environment.

The overview of an approach for a new thin glass handling strategy has been reported previously. [12,13] The approach utilizes a thin inorganic adhesion layer to temporarily 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 Â°C. Utilizing a Si handle wafer allows the thin glass to be processed leveraging existing equipment and process flows, with only a mechanical de-bond to yield finished substrates.

A key aspect of this handling solution, is that it addresses the gaps in the supply chain that have adversely affected the adoption of glass-based solutions. It is important that this solution integrate seamlessly into typical back-end processes, which includes via fill, CMP, RDL, de-bond and dicing/singulation without significant changes or upgrades required of existing process equipment. In this paper, we will describe the advances made to show the application of this temporary bond approach to leverage existing capabilities of standard processing equipment. In particular, we will show the ability to provide void free via fill using standard wafer-based approaches, such as blind via technology and ability to apply existing chemo-mechanical polishing (CMP) processes for Cu overburden removal and CMP. We will demonstrate the ability to provide top and bottom surface metallization/RDL using standard de-bond approaches as well as application of industry standard tools for dicing/singulation.