The evaluation of Young's modulus and residual stress of Cu films by NiFe/Cu bilayer film microbridge tests

This paper proposes a method to estimate the thickness limit for single- layer microbridge tests and also the thickness limit of one film on another film with known thickness for bilayer microbridge tests. To evaluate the mechanical properties of the Cu film, which could not be measured by single-layer microbridge tests, the NiFe single-layer film and NiFe/Cu bilayer film on silicon substrate are fabricated onto the microbridge by the MEMS technique. A load -deflection experiment is conducted upon the ceramic shaft adhered to the microbridge center by means of the XP nanoindenter system. From single-layer microbridge theory, Young's modulus and the residual stress of the NiFe film are deduced to be 192.74 +/- 8.10 GPa and 287.75 +/- 16.18 MPa, respectively. The data are introduced into bilayer microbridge theory, and Young's modulus and the residual stress of the copper film are calculated to be 118.71 +/- 6.54 GPa and 41.34 +/- 4.42 MPa, respectively. The experimental results correspond well with those of nanoindentation.