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 mea sure 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 hea t propagation in a specimen. Thermal waves cause both a change in the refle ctivity of the specimen and a displacement of the specimen surface. By vary ing the phase difference between the reference and signal arms of an interf erometer, a method for detecting and separating the contributions of each o f these effects has been developed. This enables the determination of the t hermal expansion coefficient of the thin film independent of substrate prop erties. Data demonstrating the application of this technique on Cu and TiN thin films are presented. [S0034-6748(00)01510-0].