Measurements of Young's modulus, Poisson's ratio, and tensile strength of polysilicon

New techniques and procedures are described that enable one to measure the mechanical properties of polysilicon films that are 3.5 mu m thick. Polysilicon is deposited onto a silicon substrate which is then etched away to leave a tensile specimen in the middle of the die. The grip ends of the structure are glued to the grips of a linear air bearing attached to a piezoelectrically actuated loading system. Strain is measured directly on the specimen with laser interferometry. The specimens are fabricated at the Microelectronics Center of North Carolina with their MUMPs process. The results of 48 tests on five different sets of MUMPs specimens yield the following material properties: Young's modulus = 169 +/- 6.15 GPa, Poison's ratio = 0.22 +/- 0.011, and tensile strength = 1.20 +/- 0.15 GPa These values have a reasonably low coefficient of variation which demonstrates the consistency of both the processing and the measurement techniques.