6  Residual Stress in TSVs

In Chapter 5 the local stress of the TSV and the effects of small TSV features were discussed, but the residual stress was given a priori as an embedded property of the material. In this chapter the residual stress is investigated, the prevailing knowledge of its origin is reviewed, and models for its calculation are presented. Based on the calculations a methodology suitable for residual-stress conscious engineering design is provided.

The discussion in this chapter is focused on metal films especially concerning their importance in TSVs. With that in mind, the development of models is much more important for unfilled TSVs, where the thin metal films’ behavior has a bigger impact on the overall stress. In filled TSVs, the thin film impact is eclipsed by the stress induced by CTE mismatch which plays the major role in determining the TSV stress. Therefore, the sections to follow study the residual stress due to the deposition of the thin metal films on the sidewall of the unfilled TSVs.

6.1 Growth of Metal Films
6.2 Residual Stress Formation
6.3 Residual Stress Calculation of a Single Droplet
6.3.1 Hoffman’s Model
6.3.2 Nix-Clemens Model
6.3.3 Freund-Chason Model
6.4 FEM Calculations of Residual Stress in Single Droplets
6.5 Residual Stress Estimation
6.5.1 One-Dimensional Volmer-Weber Growth Simulation
6.5.2 Coalescence Simulation
6.5.3 Stress Estimate
6.5.4 Summary and Conclusion