MODE OF GROWTH AND MICROSTRUCTURE OF POLYCRYSTALLINE SILICON OBTAINED BY SOLID-PHASE CRYSTALLIZATION OF AN AMORPHOUS-SILICON FILM

The structure and the morphology of crystallized amorphous silicon (a-Si) films which were deposited on glass and annealed in a conventional furnace or by rapid thermal process (RTP) are studied using transmission electron microscopy (TEM). The ellipsoidal shape of the grains is attributed to the fast solid-state crystallization along the two mutually perpendicular [112] and [110] crystallographic directions. The growth is solely based on the twin formation. The stability of the microtwins was studied by RTP and in situ TEM heating experiments. The effect of the film thickness on the preferred orientation of the grains is discussed. Very thin films exhibit (111) preferred orientation due to the strongly anisotropic rate of growth of the nuclei, which imposes an orientation filtering due to a growth velocity competition. The mode of growth of these films is compared with poly-Si films grown by low-pressure chemical-vapor deposition.