Handbook of Silicon Based MEMS Materials and Technologies

18.2. Mems Residual Stress Characterization Techniques

18.2.1. Curvature measurement

The most widely applied or acknowledged thin-film stress measurement method is the curvature measurement of beam or plate structures. As shown in Fig. 18.2, by measuring the warpage information of a structure, followed by proper conversion mechanics, it is possible to extract the stress information. Consider a composite film-substrate wafer shown in Fig. 18.3. The film thickness and Young’s modulus are d^f and E^f, respectively, and the corresponding substrate values are d^s and E^s. Stoney’s formula published one hundred years ago links the film stress and the wafer curvature as [21](18.1)

Fig 18.2. Schematic plot of curvature measurement.

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