Microtensile testing of free-standing polysilicon fibers of various grain sizes

Tensile strength and elastic modulus measurements of low-pressure chemical vapour deposited (LPCVD) polysilicon films were performed on freestanding microtensile specimens (fibers) fabricated from the films. Various annealing treatments were employed to alter the polysilicon grain size. Fibers were fabricated from films with grain sizes of 50, 100, and 500 nm. The fiber cross sectional area was 3.3 mu m³ and the gauge section was 30 mu m long. The fibers failed in a brittle fashion with tensile strengths between 2.7 and 3.4 GPa. Fibers fabricated from polysilicon with 500 nm grain size had uniform equiaxial grains and were stronger than fibers made from smaller grain size material. This higher strength can be attributed to the better interface between the 500 nm grains as a result of the annealing process. The average elastic modulus of the fibers was 175 GPa.