Low temperature activation of dopants which were doped using ion mass doping system in amorphous silicon(a-Si) thin films was investigated. With a 20.angs.-thick Ni film on top of the a-Si thin film, the activation temperature of dopants lowered to 500.deg. C. When the doping was performaed after the deposition of Ni thin film on the a-Si thin films (post-doping), the activation time was shorter than that of dopants mass, the activation time of the dopants doped by pre-doping method increased. It turned NiSi2 formation, while the decrease of activation time was mainly due to the enhancement of the NiSi2 formation by mixing of Ni and a-Si at the interface of Ni and a -Si thin during the ion doping process.