Evaluation of Thin Film Mechanical Properties by Means of Electrical Test Methods
Nicholas Barbosa, Robert R. Keller, David T. Read, Richard P. Vinci
The ability to measure the mechanical properties of thin films and small scale structures is essential in designing reliable components at the micro- and nano-scales. It is known that the mechanical properties of thin film materials deviate from relations typically used to describe bulk materials and although a number of methods are available to measure mechanical properties, a measurement technique not limited to research laboratories has yet to be established. In this work we compare two test types: a microtensile test and an electrical a.c. thermomechanical fatigue test. Tests are performed on structures co-fabricated from thin film Al deposited on a Si wafer to ensure comparable mechanical properties. The films have a 220 nm grain diameter and a thickness of 1.853 υm. The freestanding microtensile test is used as a standard for comparison, and through it a modulus of elasticity of 67.8 ± 5.6 GPa, a yield strength of 143.09 ± 12.6 MPa, and an ultimate tensile strength of 238.6 ± 3.7 MPa were determined. Through the use of a modified Basquin relation, an ultimate tensile strength of 264.17 MPa was determined from the a.c. thermomechanical fatigue test. The close agreement between measured ultimate tensile strengths demonstrates the ability to determine mechanical properties of thin films through electrical testing methods.