Locally induced stress in stacked ultrathin Si wafers: XPS and μ-Raman study

Induced local stress arising from local deformation of top silicon die in the vertically stacked LSI die has been investigated via x-ray photoelectron spectroscopy (XPS) and micro-Raman spectroscopy (μRS). The large positive shift in the core level Si-2s and Si-2p XP spectra for the thinned die revealed that thinned dies were under heavy stress/strain even before stacking. The core level binding energy shift, ΔEb for Si-1s core level and the relative chemical shift ΔEr for Si in the vertically integrated die system showed that the stacked Si dies were under different stresses in the μ-bump and the bump-space regions. It was also inferred from the μRS results that the stacked 10 μm-thick-Si dies were under large tensile strain of >1.5 GPa and a relatively small compressive stress of ∼0.5 GPa in the μ-bump and bump-space region, respectively.