Estimation of Young's Modulus for Polysilicon Thin Film by Finite Element Analysis

The Young's modulus of a polysilicon thin microelement was evaluated using the previously developed mechanical testing system for thin tensile microelements. The tested part of the specimen is 250 μm in length, 10 μm in width, 3.8 μm in thickness. The Young's modulus of the tested polysilicon thin film was 133±10 GPa. To analyze the effect of the crystal orientations and the grain size on the Young's modulus, two-dimensional finite element models in plain strain condition were developed using a Voronoi structure. The number of grains in a model of a 10 μm square area was changed from 23 to 1200. The crystal orientation of the film was analyzed by means of an electron back-scattering diffraction pattern (EBSP) method. The front surface of the film did not have the oriented structure. Therefore, random crystal orientation was given to each grain of the FEM models. When the number of grains increased, the Young's modulus converged on about 170 GPa and its scatter caused by the different sets of the random orientation was reduced. However, the Young's modulus obtained by the FEM analysis was larger than the value obtained by the tensile tests.