Simultaneous measurement of Young’s modulus, Poisson ratio, and coefficient of thermal expansion of thin films on substrates

Abstract

A method of measuring the Yong’s modulus, Poisson ratio, and coefficient of thermal expansion (CTE) is presented. The method uses a wafer curvature technique to measure thermal stresses of thin films of the same material deposited on two different substrates, one isotropic and the other thermomechanically anisotropic. By analyzing the thermal stress data as a function of temperature, the Young’s modulus, Poisson ratio and CTE can be simultaneously determined. The method is demonstrated for Al (0.5 wt % Cu) and Cu thin films by performing measurements on (100) Si wafers and Y-cut single-crystal quartz wafers. The CTE, Young’s modulus, and Poisson ratio are found to be 24.3 ppm/°C, 58.9 GPa, and 0.342, respectively, for Al (Cu) thin film, and 17.7 ppm/°C, 104.2 GPa, and 0.352, respectively, for Cu thin film. They are in good agreement with those measured by other methods. This method is generally applicable to other on-wafer films with in-plane isotropy.