µ-Raman spectroscopy and FE-modeling for TSV-Stress-characterization

Display Omitted We model thermo-mechanical stresses in silicon after annealing of TSVs.Results deliver detailed stress information of specific stress components.FEM demonstrates that the induced stress distribution is complex and cannot be described by a uniaxial stress thesis.Tensions decrease with increasing distance to the TSV.Simulation is validated by micro Raman spectroscopy measurements. In this paper thermo-mechanical stresses generated by TSV annealing are the center of interest. For this reason TSV die samples underwent annealing at 250?C for 2h. In order to characterize the stress state after annealing µ-Raman spectroscopy (µRS) line scans were carried out subsequently using a 442nm laser. Then the respective spectra were fitted with a Lorentz function and the associated peak shifts were calculated. In general these results can be used to identify regions of mechanical tension. Unfortunately, µRS results do not allow any differentiation of the stress tensor components. Therefore a finite element model was developed to determine the stress tensor components after annealing. The FE-model was supplemented by a Matlab script, which converted stress data from simulation into Raman shifts using a general hypothesis. Further on physical aspects like penetration depth and laser spot size were taken into account. So the evaluation moved from single node results to a constrained section similar to the laser excited region in a µRS measurement. Proceeding this way allowed the adaption of FE results to µRS measurement properties. This enabled a bilateral validation of measurement and simulation.In summary our paper contributes valuable results for the TSV stress characterization and demonstrates further progress in µRS measurements in combination with FEM.

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