The evaluation of Young's modulus and residual stress of copper films by microbridge testing

This paper investigates the variation of the deflection and maximum stress of copper film microbridge in a wide range of length, thickness, elastic modulus and residual stress by both large and small deflection theories of microbridge testing. The limits of deflection and load for the microbridge samples to be deformed elastically are determined by the assumption that the maximum stress could not be larger than the yield strength. Furthermore, the deflection and load limits of small deflection theory are decided by setting a threshold preset for the normalized deflection and maximum stress difference between large and small deflection theories. Based on the results above, the microbridge dimensions are chosen and the deflection range suitable for the small deflection theory is calculated. The copper film microbridge samples electroplated on silicon substrate are fabricated by MEMS and the microbridge testing is conducted with nanoindenter XP system. From the small deflection theory, the Young's modulus and residual stress for the electroplated copper films is calculated, and it is 115.2 GPa and 19.3 MPa, respectively.