The stress in silicon surrounding a tungsten-filled through-silicon via (TSV) is measured using confocal Raman microscopy line scans across the TSV both before and after etch removal of an oxide stack used as a mask to define the TSV during fabrication. Stress in the silicon arose in response to both athermal deposition and thermal expansion mismatch effects. The complex three-dimensional stress and strain field in silicon surrounding the TSV is modeled using finite element analysis, taking into account both athermal and thermal effects and the elastic anisotropy of silicon. Comparison of the measurements and model results shows that no one component of the stress tensor correlates with the Raman peak shift generated by the deformed silicon. An analysis is developed to predict the Raman shift in deformed silicon that takes into account all the components of the stress or strain tensor; the results of the model are then used as inputs to the analysis for direct comparison with measured peak shifts as a function of distance from the TSV. Good agreement between the measured and predicted peak shifts is obtained for the case of the intact oxide stack. A discrepancy between the measured and predicted shifts was observed adjacent to the TSV with the oxide stack removed; further modeling suggests the discrepancy is explained by the formation of a small void at the TSV-silicon interface during etching. The combined measurement-modeling approach serves to both validate the model, in this case for TSV design, and to extend the measurement capability of confocal Raman microscopy to complex stress fields.

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Thermo-mechanical stress of tungsten-filled (W-fill) through-silicon-via (TSV) is strongly depending on via shape, size and inter-via spacing, which places constraints on TSV design, including 2-D integrated circuit layout and 3-D structure profile. This paper summarizes these constraints and co-relations among thick (up to 1.2μm) tungsten (W) film, W-fill TSV, and surrounding silicon structures, using Flexus bowing measurement, Wright etch method, and also 3-D TSV stress simulations. In this study, the stress was found to be primarily tensile, and tended to be much higher along the longitudinal ends of the TSV compared to the longitudinal side wall. For an isolated TSV of given width and depth: with 30μm length the stress is 45% greater compared to the case of 7μm length. For an array of TSV with given length, width, and depth: larger spacing along the longitudinal axis (length directions) resulted in 35% lower stress at the longitudinal ends of the TSV, while smaller spacing along the transverse axis (width directions) of the TSV resulted in a 46% lower tensile stress. However, along the longitudinal side walls, the tensile stress increases by 200 MPa as the spacing along the transverse axis decreases between neighboring TSV.

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