This paper reports on the tensile testing of single crystal silicon (SCS), whose specimen surface was intentionally oxidized, and the effect of the oxide thickness on the mechanical properties in order to investigate the fatigue fracture mechanism under cyclic loading. SCS specimens were fabricated from silicon-on-insulator (SOI) wafer with 3-μm -thick device layer and oxide layer were grown to the specimens using thermal dry oxidation at 1100 °C. The specimen test part was 120 or 600 μm long and 4 μm wide. Quasi-static tensile testing of SCS specimen without oxide layer, with 100-nm-thick oxide, and with 200-nm-thick oxide was performed. As the results, the fracture origin location changed from the surface of the specimen of SCS without oxide to inside of silicon of oxidized specimen. This change may be caused by the smoothing of the surface and formation of oxide precipitation defects in silicon during oxidation. The estimated radius of the defects in specimen with 100 -nm-thick oxide and with 200-nm-thick oxide was 26 nm and 45 nm, respectively, which is well agreed with the fracture-initiating crack sizes calculated from the measured strengths.
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