Crystallization-Induced Stress in Amorphous Silicon Thin Films

A New stress development mechanism in thin films, crystallizatin-induced stress, is discussed experimentally in P-doped amorphous silicon thin films. P-doped amorphous silicon thin films are deposited on thermally oxidized silicon wafers at 520°C using the CVD technique. The thickness of the oxide is 0.1 μm, and that of amorphous silicon is about 550 nm. The crystallization process, i. e., nucleation and growth of polycrystalline silicon, in the amorphous silicon thin films is observed using a scanning laser microscope. During the crystallization process of the amorphous silicon film, the silicon film shrinks and a large tensile stress of about 1000 MPa occurs in the film. The crystallization temperature of the P-doped amorphous silicon film decreases with higher P concentration. However, the crystallization-induced stress does not depend on the doped-P concentration. The developed stress decreases with high-temperature annealing at over 700°C. The stress relaxation ratio becomes higher in the higher P-doped films.