Practical polycrystalline silicon thin-film transistors need a low-tem
perature doping technique. Ion shower doping with a main ion source of
P2Hx (x = 1, 2,...) was studied. This technique implants a molecule i
n the polycrystalline silicon surface with a low acceleration voltage.
A critical impurity density from polycrystalline phase to amorphous p
hase for phosphorus in polycrystalline silicon of 2.0 x 10(20) ions/cm
3 was found. Sheet resistance with ion shower doping was lower than wi
th conventional ion implantation at low temperature. This is a result
of an increase in sheet carriers, because the low-temperature recoveri
ng of defects is done by molecular implantation and hydrogen atoms com
pensate defects. Implanted polycrystalline Si with a Hall mobility of
5 cm2/V s was obtained.