Polycrystalline silicon layers for micromechanical applications: Stress profile analysis

Stress and stress gradient in polycrystalline silicon films, as active micromechanical layers, are analysed taking into account the obtention technology, doping procedure and thermal annealing treatments. Micro-Raman and X-ray diffraction sin(2) psi plots are discussed as experimental techniques to obtain stress and stress profile information before performing the microstructure fabrication run as well as to obtain data about the microscope mechanisms which are responsible for the mechanical behaviour of these layers after releasing them from the silicon dioxide sacrificial layer. Influences of the thermal treatments, annealing ambients and doping techniques on the stress characteristics are discussed for thin layers, 2 mu m LPCVD films, and chick layer, 10 mu m epipolysilicon films. From the results obtained, these technological steps are considered and discussed as stress engineering elements to control the final mechanical behaviour of the polycrystalline silicon layers which can present stress gradients lower than several megapascals per micrometre. (C) 1997 Elsevier Science Ltd.