Effect of TSV density on local stress concentration: Micro-Raman spectroscopy measurement and Finite Element Analysis

In order to develop ’More-than-Moore’ technologies, interconnection by Through-Silicon Via (TSV) is a promising candidate, but TSV leads to fabrication and mechanical issues. In this paper, mechanical stress analysis in silicon surrounding 50 μm thick TSVs is performed. A calibrated micro-Raman spectroscopy (μRS) is used as a non destructive method to determine local silicon stress. Results indicate that when a curvature radius is applied on 50 μm thick rectangular silicon lamella containing TSVs, a local mechanical stress is generated around TSVs. For non-metalized TSVs, the maximal stress is three times higher in the longitudinal direction compared to the transversal direction. Furthermore this local maximal stress depends linearly on the geometrical parameter R which is the ratio of via diameter by via-to-via spacing, and its intensity increases with R value. Micro-Raman Spectroscopy measurements were confirmed by Finite Element Analysis (FEA). Further FEA investigations of maximal stress when TSVs are lined with copper revealed that this stress level is reduced even though its linear dependence to the geometrical ratio R is conserved. The aim of the present work is thus to define design rules for optimal mechanical flexibility in a system that contains TSVs.

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