AFM and TEM Examination of Surface Grains in LPCVD Silicon Films

Abstract

AbstractPolycrystalline silicon is an important technological material in microelectronics, and more recently in microelectromechanical systems (MEMS). For MEMS applications polysilicon films with residual tensile stress are often used, requiring film growth in the transition zone from 550-600°C. In this study polysilicon films were grown in a hot walled LPCVD reactor at 590°C to a thickness of 450 nm. The tensile as-deposited stress in the wafers was found to decrease with distance from the reactor front and served as a marker for the changing microstructure and surface roughness of the film as measured by Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM). It was found that the surface contained a high density (≍30 /µm2) of grains that protruded 30 nm above the mean film surface. The size and volume of these grains increased linearly with decreasing stress until the surface saturated and became uniformly rough. The nature of these surface grains, their spatial characteristics, and their annealing behavior is discussed.