Characteristics of top-gate polysilicon thin-film transistors fabricated on fluorine-implanted and crystallized amorphous silicon films

Abstract

This paper presents a comprehensive study on the characteristics of n- and p-channel polycrystalline-silicon (polysilicon) thin-film transistors (TFTs) fabricated on fluorine-implanted-then-crystallized amorphous silicon films. Amorphous silicon films of two thicknesses were implanted with different energies and various dosages of fluorine, and studied using transmission electron microscopy (TEM) and secondary-ion mass spectrometry (SIMS). The electrical characteristics of TFTs fabricated 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 devices were improved by the fluorine implantation thanks to the enhanced grain size and the fluorine passivation effect. For the p-channel device, the fluorine implantation did not improve the subthreshold swing and 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.