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The uncontrolled development of stress within MEMS deposited and processed films can be detrimental for both device performance and reliability. This work focuses on combining the data from previously reported strain measurements obtained from mechanical test structures with new nano-indentation measurements of Young's modulus on both micromachined films and cantilevers. Both strain and Young's modulus data are then used to produce arguably the first quantitative wafer-level stress mapping of residual stress in micromachined materials. Results show significant local variation and possible correlation between Young's modulus and percentage of iron in the film. The measured values for the two test wafers, namely Young's modulus and residual stress, fall within the range of ~30 to ~180 GPa and ~50 to ~220 MPa, respectively. Young's modulus measurements on cantilevers show a consistent ~20% difference with respect to traditional indentation measurements, suggesting that this setup may help reduce or remove the influence of the substrate.
Date of Conference: 19-22 March 2012