Micro-structures of BF2+- and As+-implanted polycrystalline silicon thin films of various thicknesses and heat treatments

Characterization of annealed BF2+- and As+-doped polycrystalline silicon (polysilicon) films is presented. Effects of heat treatment, doping concentration, and thickness of film on the grain size and mobility of polysilicon films are investigated and discussed. By using transmission electron microscopy (TEM), it is found that the grain size, effective carrier concentration, and carrier mobility of a polysilicon thin film increases with increasing film thickness. Our results show that a high concentration of As dopant could enhance the recrystallization of the polysilicon films. Heavily As+-doped samples were seen to have a relatively larger grain size compared to the lightly doped film. The maximum grain size of about 278 nm can be realized in a polysilicon film with 150 nm in thickness. In contrast, the B dopant has a negligible effect on the recrystallization of polysilicon films. With increasing film thickness and thermal annealing temperature, a high performance polysilicon film with high mobility and grain size can be obtained.