Fatigue Testing of Polycrystalline Silicon Thin-Film Membrane Using Out-of-Plane Bending Vibration

This paper describes a new fatigue testing method for polycrystalline-silicon (polysilicon) thin-film membrane to evaluate its mechanical reliability not affected by surface roughness of etched sidewalls. The test specimen is a thin membrane consisting of polysilicon, silicon dioxide, and silicon ni...

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Bibliographic Details
Published inJapanese Journal of Applied Physics Vol. 51; no. 11; pp. 11PA02 - 11PA02-7
Main Authors Tanemura, Tomoki, Yamashita, Shuichi, Wado, Hiroyuki, Takeuchi, Yukihiro, Tsuchiya, Toshiyuki, Tabata, Osamu
Format Journal Article
LanguageEnglish
Published The Japan Society of Applied Physics 01.11.2012
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Summary:This paper describes a new fatigue testing method for polycrystalline-silicon (polysilicon) thin-film membrane to evaluate its mechanical reliability not affected by surface roughness of etched sidewalls. The test specimen is a thin membrane consisting of polysilicon, silicon dioxide, and silicon nitride films with a circular weight at the center, and its outer edge is supported by a square frame. Stress on polysilicon for fatigue test is applied by deformation of the membrane generated by oscillating the weight in the out-of-plane direction near the resonant frequency. The polysilicon film fractured by fatigue damage accumulated by the cyclic stress. Stress and number of cycles to fracture ($S$--$N$) plots were well formulated on the basis of Weibull statistics and Paris' law. Weibull modulus and fatigue index of the 250-nm-thick polysilicon film were 19.2 and 21.8, respectively. These parameters make it possible to predict the lifetime of polysilicon thin-film membrane under arbitrary cyclic stress.
Bibliography:Schematic setup of mechanical reliability tests for a specimen with a membrane. Details of test specimen. Calculated maximum stress on membrane as a function of weight displacement. Inset figures are (a) displacement and (b) Mises stress of membrane (calculated with a quarter FEM model). Calculated resonant frequency as a function of vibration amplitude. Process flow to fabricate specimens. (a) Displacement of weight and frame oscillated at 300 Hz. (b) Displacement at the point of fracture oscillated at 1.5 kHz. Dependency of initial fracture stress on polysilicon film thickness calculated from fracture displacement; error bars indicate standard deviation. Surface profile of polysilicon films obtained by AFM; $R_{\text{a}}$ is the roughness average. Specimen (a) before test and (b) after fracture. (c) Oblique view of fractured specimen at the fracture origin obtained by SEM. Weibull plots of initial fracture strength of polysilicon membrane. (a) $S$--$N$ plots of fatigue lifetime of polysilicon membrane. (b) $S$--$N$ plots normalized with initial fracture strength. Weibull plots of fatigue lifetime of polysilicon membrane. Normalized $S$--$N$ plots of fatigue lifetime of polysilicon membrane with fitting curve.
ISSN:0021-4922
1347-4065
DOI:10.1143/JJAP.51.11PA02