NON-MASS-SEPARATED ION SHOWER DOPING OF POLYCRYSTALLINE SILICON

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 x 10(20) ions/cm3 was 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.