On the measurement of residual stress in thin films

This work reports a comparative study on three curvature based techniques for stress measurement in thin films, including double crystal diffraction topography (DCDT), profilometry, and laser scanning technique (LST). These techniques measure different physical quantities. In the former case, the curvature of crystal lattice planes is assessed while in the latter two cases, the curvature of physical surface of a sample is measured. The current experiments use these three techniques to determine the quantities of interest for a variety of films deposited on Si (100) wafers. In general, profilometry and LST produce similar results on surface curvature. For specimens where the residual stresses produces large curvatures of both types (lattice curvature and surface curvature), the results by DCDT and LST agree fairly well. When small to moderate curvatures are present, the two methods deviate to varying degrees on absolute curvatures. Nevertheless, DCDT and LST generally yield similar results on differential curvatures, i.e., the stress induced curvature differentials. When proper consideration is taken for the inherent limits of each technique, both DCDT and LST can be used as valid procedures for stress measurement in thin film-substrate systems.