A Label-Free Measurement Method for Plane Stress States in Optical Isotropic Films with Spectroscopic Ellipsometry.

Background: Stress measurement for thin films is crucial in a variety of fields such as in semiconductor manufacturing, the optoelectronics industry, and biomedical science, among others. However, most measurement methods require surface treatment of the thin film. Objective: A label-free measurement method for plane stress states in optical isotropic thin films based on spectroscopic ellipsometry analysis is proposed and verified in this paper. Methods: The proposed method is based on the modulation of the stress-optic effect on reflected spectroscopic ellipsometry. A theoretical model is established to describe the relation between all components of the plane-stress state and the classic ellipsometric parameters (Ψ, Δ). An algorithm is developed to determine all components of a plane-stress state by fitting the model to the experiment data. Results: In the verification experiment, we determined the plane stress state of a Cu film coated on a PI (polyimide) substrate. The results show a reasonable agreement between the experimental measurements from spectroscopic ellipsometry and the theoretical analysis based on the applied loading. Conclusion: The results prove that our method can effectively measure the plane stress state of optical isotropic thin films. [ABSTRACT FROM AUTHOR]