Non-mass-separated ion shower doping of polycrystalline silicon

Abstract

Practical polycrystalline silicon thin-film transistors need a low-temperature doping technique. Ion shower doping with a main ion source of P2Hx (x=1,2,...) was studied. This technique implants a molecule in the polycrystalline silicon surface with a low acceleration voltage. A critical impurity density from polycrystalline phase to amorphous phase for phosphorus in polycrystalline silicon of 2.0×1020 ions/cm3was found. Sheet resistance with ion shower doping was lower than with conventional ion implantation at low temperature. This is a result of an increase in sheet carriers, because the low-temperature recovering of defects is done by molecular implantation and hydrogen atoms compensate defects. Implanted polycrystalline Si with a Hall mobility of 5 cm2/V s was obtained.