Correlation of PVD deposition parameters with electrical and mechanical properties of coated thin-glass compounds

In microelectronic applications the use of ultra-thin glass (UTG) to substitute materials like polymers or silicon as substrate or encapsulation materials is very interesting as glass outperforms those materials in several aspects. In this paper, process parameters of different uncoated and, with 100 μm indium tin oxide (ITO), coated glass substrates are correlated to their electrical, optical and mechanical properties. Fracture strength has been determined by applying a Ball-on-Ring test setup optimized by finite-element simulation to take non-linear effects into account which result from the UTG aspect ratio. Differences in fracture strength between front and backside could be shown for the uncoated substrates. Coating the UTG substrates creates intrinsic stresses, deforms the glass and therefore reduces the fracture strength significantly. These intrinsic stresses and the warpage after the coating process has been determined by wafer bow measurements using white-light interferometry (WLI). The hardness of the ITO coating has been determined using nanoindentation and correlated to the intrinsic stresses and warpage determined before. Furthermore a correlation to the oxygen concentration during the sputtering process could be found. WLI measurements have also been used to measure the substrate deformation before the ITO coating process. It was found, that already the different uncoated substrates show very different behaviors.