Separation of thermal wave induced displacements and thermoreflectance variations using a rotated beamsplitter cube interferometer

A rotated beamsplitter cube interferometer has been developed which can measure both the change in reflectivity and the displacement of nontransparent thin films caused by thermal waves. Thermal waves are used to characterize material properties, especially those of thin films, by monitoring the heat propagation in a specimen. Thermal waves cause both a change in the reflectivity of the specimen and a displacement of the specimen surface. By varying the phase difference between the reference and signal arms of an interferometer, a method for detecting and separating the contributions of each of these effects has been developed. This enables the determination of the thermal expansion coefficient of the thin film independent of substrate properties. Data demonstrating the application of this technique on Cu and TiN thin films are presented. [S0034-6748(00)01510-0].