CHARACTERISTICS OF TOP-GATE POLYSILICON THIN-FILM TRANSISTORS FABRICATED ON FLUORINE-IMPLANTED AND CRYSTALLIZED AMORPHOUS-SILICON FILMS

This paper presents a comprehensive study on the characteristics of n- and p-channel polycrystalline-silicon (polysilicon) thin-film transis tors (TFTs) fabricated on fluorine-implanted-then-crystallized amorpho us silicon films. Amorphous silicon films of two thicknesses were impl anted with different energies and various dosages of fluorine, and stu died using transmission electron microscopy (TEM) and secondary-ion ma ss spectrometry (SIMS). The electrical characteristics of TFTs fabrica ted on the films were correlated with the results of TEM and SIMS, It was found that field-effect mobilities of both n- and p-channel device s were improved by the fluorine implantation thanks to the enhanced gr ain size and tile fluorine passivation effect. For the p-channel devic e, the fluorine implantation did not improve the subthreshold swing an d even degraded it after hydrogenation. This result was thought to be caused by the fluorine-induced negative charges in oxides. However, a thin active layer and a deep implantation reduced this degradation.