In order to clarify the stress concentration and surface roughness effect on strength of the polycrystalline silicon (poly-Si) structure, bending tests of poly-Si microcantilever beam specimen and surface roughness measurement is performed. The bending test results are analyzed by means of maximum stress at the notch root calculated by FEM models, and it is found that this approach cannot describe the test results. Therefore, modified approach is taken into account by use of two parameters that are the maximum stress and area where stress is larger than 50% of the maximum stress, which indicates stress extension around the position of maximum stress representatively. By this two parameters approach, the test results are explained quantitatively and a strength design chart for stress concentration area of the poly-Si structure is obtained. On the other hand, relationship between strength and surface roughness are confirmed and useful information for the process quality control are obtained.

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