Simultaneously determining Young´s modulus, coefficient of thermal expansion, Poisson ratio and thickness of thin films on silicon wafer

A method is demonstrated to simultaneously determine Young´s modulus (E), coefficient of thermal expansion (α), Poisson ratio (v), and thickness (t) of thin films on a silicon wafer. A digital phase-shifted reflection moire (DPRM) technique was adopted to record the warpage slope of the film/wafer composites under temperature change. These data were used to compare with the ANSYS analysis, and a genetic algorithm (GA) was employed to search for the optimal mechanical parameters of the films. In the first experiment, 1.20-μm thick copper was sputtered on a 4-inch silicon wafer. While the determined film thickness was in good agreement with the measured value, the deviation in E, α and v was significant. The micro-structural difference between the bulk material and the thin film, and oxidation on the film surface were considered to be the two major causes to this deviation. In order to verify the determined mechanical parameters of this 1.2-μm Cu film, an additional 2.4-μm Cu film was sputtered on the Cu/Si wafer and the determined mechanical parameters of this additional Cu film were identical to the data obtained in the 1.2-μm film, which demonstrated the validity of the developed method.