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Mechanical strength study of SiO2 isolation blocks merged in silicon substrate

Quasi-static bending, compressive, tensile and fatigue tests of freestanding thermally oxidized crystal silicon microelements fabricated by the deep-reactive-ion etching process were performed to evaluate the strength and the reliability of structures. These structures serve as bearings and electrical isolation for microelectromechanical systems. The tests were conducted at device level using a specially designed electromagnetic actuator based on a testing machine (load range: 1 mN–1 N, accuracy: ± 0.08 mN) which enables mechanical testing of microelements. We have developed a method to calibrate an actuator using the silicon cantilevers on the microscale. A finite element model of the test structure is proposed. This model is used to calculate the displacements and stresses produced by an applied load force. Isolation structures are fractured from both the front and back sides of the wafer, and fracture strength results are compiled for each of these cases. It was found that the tensile strength of the structures is 200 MPa and the ultimate bending stress is 550 MPa. Data on strength and failure stress as found in the study may be very important for reliability evaluation of isolation merged in single crystal silicon wafer.