A method to enhance grain size in polysilicon films while avoiding
formation of hemispherical grains (HSG) is disclosed. The method begins
by depositing a first amorphous silicon film, then depositing silicon
nuclei, which will act as nucleation sites, on the amorphous film. After
deposition of silicon nuclei, crystallization, and specifically HSG, is
prevented by lowering temperature and/or raising pressure. Next a second
amorphous silicon layer is deposited over the first layer and the nuclei.
Finally an anneal is performed to induce crystallization from the
embedded nuclei. Thus grains are formed from the silicon bulk, rather
than from the surface, HSG is avoided, and a smooth polysilicon film with
enhanced grain size is produced.