Laminating thin glass onto glass carrier to eliminate grinding and bonding process for glass interposer

Abstract

Interposer fabrication processes are critical techniques in 3D-IC integration, providing the short interconnection among different stacked chips and the substrate [1]. 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 as well as the ability to provide a low cost solution [2]. In this investigation, another cost reduction concept of through glass via (TGV) wafer processing is being studied. By leveraging current semiconductor equipment and know-how, we bond TGV wafers onto glass carriers as shown in Figure 1, the TGV wafer thickness is directly 100um and center diameter (CD) of through glass via is 30 μm. This approach provides a method to temporarily bond these TGV wafers to glass carriers enabling handling through processes such as via fill and surface metallization. The ability to form glass at the target 100 um thickness and provide through holes and thus avoid backgrinding processes provides substantial opportunity to save costs and avoid yield loss. The TGV interposer wafer is bonded with a glass carrier by a polymeric bonding material. The bonding material must be compatible with surface materials as well as good step coverage to void-free bonding [3]. Most importantly, the bonding material shall remain stable and good resistance in harsh thermal and chemical environments to protect interposer at all time [4]. The thermal stability and characteristics of the bonding material used in this study as shown in Figure 2, is important to maintain low warp. Finally, the treated glass carrier is released from the bonding material by a laser de-bond method. The laser debond method is known to have several benefits such as (a) high throughput: possible to de-bond one pair within 30s (b). low temperature: UV range wavelength does not generate heat in the de-bonding process (c). zero force de-bon ding: after laser scanning, the carrier can be lifted off directly (d). process efficiency: laser release layer is a spin-on material, so only a spin bowl is required. Here we use 308 nm laser and this wavelength also has the benefit with less impact to the device.