Characterization of Polycrystalline Silicon-Germanium Film Deposition for Modularly Integrated MEMS Applications

The deposition ofin situboron-doped polycrystalline silicon-germanium (poly-SiGe) films in a conventional low-pressure chemical-vapor deposition reactor has been characterized using the design of experiments method. The dependencies of deposition rate, resistivity, average residual stress, strain gradient, and wet etch rate in hydrogen peroxide solution are presented. Structural layer requirements for general microelectromechanical system applications can be met within the process temperature constraint imposed by complementary metal–oxide–semiconductor (CMOS) electronics. However, residual stress and strain gradient requirements for inertial sensor applications will be difficult to meet with a single homogeneous layer of poly-SiGe that is about 2μmthick. By correlating stress depth profile measurements with cross-sectional transmission electron microscopy images, we conclude that the large strain gradient is due to highly compressive stress in the lower (initially deposited) region of the film. For films deposited at very low temperature (near the range of amorphous film deposition),in situboron doping enhances film crystallinity and reduces the strain gradient.2006-0066