Thermal stress analysis and characterization of themo-mechanical properties of thin films on an elastic substrate

Abstract

This chapter presents a comprehensive review of the thermally induced stress in multilayer thin films within both the elastic and elastic-plastic deformation ranges and several approaches to determine the thermomechanical properties of thin films. The elastic analysis based on the linear strain assumption results in the closed-form solutions and approximations (for very thin films). Subsequently, the review is extended into the elastic-plastic deformed films in bilayer structures. Closed-form solutions of the maximum, average, and minimum film stresses and curvatures are discussed in details for plastically deformed films. The difference among the maximum stress, average stress, and Stoney stress in films is systematically revealed. As an example, the result of a case study reveals that the yield start point may be estimated as a linear function of temperature in the elastic-plastic deformation range. A newly developed simple approach to determine the values of five thermomechanical properties of thin films, namely, the Young’s modulus, the coefficient of thermal expansion, yield start stress, strain hardening modulus, and Poisson’s ratio, is presented in details, together with some simple and generic approaches for the characterization of thin films with nonlinear stress versus strain relationship and/or temperature-dependent material properties. In the case of very thin films, analytical solutions are available. These new approaches and solutions are applied to investigate the moduli of metallic films. The film thickness effect on the modulus of Ag films is confirmed. The critical role of a compressive stress in thin TiO2 layer atop NiTiCu film in the reversible trench phenomenon is identified.