Microstructural observations of LPCVD double layer polysilicon thin film tensile specimens

The vast majority of micro electro-mechanical systems fabricated today depend on polycrystalline silicon thin films for structural support. Studies involving the mechanical performance of these thin films have progressed to the point where the elastic properties and tensile strength of the films can routinely be measured using a specially designed microsample tensile testing machine. However, a fundamental understanding to predict the mechanical behavior of the polycrystalline silicon films requires that these experimental measurements be complemented with detailed observations of the underlying thin film microstructure. This paper describes some of the plan view and cross-section transmission electron microscope observations that have been performed on different deposition runs of double layer polycrystalline films obtained from the Microelectronics Center of North Carolina. The emphasis has been placed on determining the flatness and dimensions of the polycrystalline films, grain morphology and distribution, texture, and dislocation substructure and microtwinning in the undeformed films.