Micromechanical Investigations of Silicon and Ni-Ti-Cu Thin Films

Residual stress, microstructure, and mechanical properties of low pressure chem cal vapor deposited polycrystalline silicon (undoped and phosphorus doped), selectively grown homoepitaxial silicon, and shape memory Ni-Ti-Cu films are investigated. Different methods for measuring residual stress in films, including substrate curvature and micro-machined strain gages, are employed, and the various models concerning film stress measurements are reviewed and evaluated. Analytical approaches for modeling residual stress in thin films are also presented. Residual stress in polycrystalline silicon, including the through-thickness gradient in stress, is correlated directly with the evolution of film microstructure, studied with transmission electron microscopy and x-ray diffraction. Mechanical degradation of thin polycrystalline silicon films upon exposure to hydrofluoric acid also is reported.
The stress state required to induce experimentally observed (311) defects in selectively grown epitaxial silicon structures is determined using three-dimensional analytical and finite element modeling. Finally, mixed-sputter deposition of Ni-Ti-Cu shape memory films is demonstrated to provide increased compositional flexibility, and the incorporation of copper is shown to reduce compositional sensitivity of the shape memory effect. The shape memory characteristics, determined with temperature controlled substrate curvature measurements, are shown to be comparable to bulk alloys, with transformation temperatures just above body temperature, a 10 degrees hysteresis between heating and cooling, and up to 330 MPa recoverable stress
George C. Johnson
Kyriakos Kornvopoulos
Publication date: 
March 30, 1994
Publication type: 
Ph.D. Dissertation
Krulevitch, P. A. (1994). Micromechanical Investigations of Silicon and Ni-Ti-Cu Thin Films. United States: University of California, Berkeley.

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