During low temperature (below 450°C) annealing, the sheet resistance of phosphorus implanted poly-Si thin films (film thickness : 50nm) decreased to lE+3Ω/square. The sheet resistance after annealing decreased with annealing time and became lower when the dosing level was high enough. At the dose of 8E+14 ions/cm2 we obtained a sheet resistance of 1E+3Q/square by annealing at 450°C for 180min. We analyzed ellipsometry data assuming a two-layer model where the surface layer consists of a-Si and the lower layer of poly-Si. This analysis indicated that the surface of implanted films was amorphized by ion implantation and the amorphized layer thickness increased with dosing level. Also, it turned out that the lower poly-Si layer thickness increased from 30nm to 50nm after annealing accompanied by the conversion of a-Si layer to poly-Si layer. During annealing at low temperature, activation of phosphorus ions implanted into poly-Si and recrystallization of a-Si took place simultaneously and the sheet resistance after annealing decreased with the increase in thickness of the recrystallized region.