Polycrystalline silicon recrystallized with excimer laser irradiation and impurity doping using ion doping method

Abstract

Polycrystalline silicon (poly-Si) thin films having large grain size have been obtained by XeCl excimer laser annealing of a-Si deposited by plasma enhanced chemical vapor deposition on SiNx. The grain size of poly-Si reaches to about 300 nm with excimer laser irradiation around 500 mJ/cm2. For excimer laser irradiation from 500 to 600 mJ/cm2, instead of further enlargement of grains, amorphous regions appear and increase in the grains. Most of the Si layer becomes an amorphous state at pulse energy density over 600 mJ/cm2. On the other hand, impurity implantation to a-Si layers using non-mass-separated ion doping equipment and a subsequent activation step with excimer laser irradiation enable us to obtain recrystallized poly-Si layers having low resistivity. By using ion doping and excimer laser annealing, we have obtained excellent n-channel thin film transistors, the field effect mobility in excess of 40 cm2/V s and the ON/OFF current ratio of more than 106, respectively.