Effects of Forming Gas Annealing on the Recovery of Radiation Damaged Power MOSFETs

• Main Authors: Lee-Shian Jeng, 鄭禮賢
• Other Authors: Mao-Chieh Chen
• Format: Others
• Language: en_US
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/95883309951536144600

碩士 === 國立交通大學 === 電子工程系 === 91 === This thesis study investigates the radiation effect of power MOSFETs as well as the forming gas annealing effect on the recovery of the radiation damaged devices. It is found that Co-60 irradiation resulted in threshold voltage (Vth) shift toward the negative voltage direction and the increase of sub-threshold swing, which are due to, respectively, the generation of radiation induced positive oxide charge and interface trapping states. However, the radiation induced oxide trap density is much higher than the radiation induced interface trap density, particularly for the devices irradiated to a higher dose. Thus the trapped oxide charges play a dominant role in determining the radiation induced threshold voltage shift. The Co-60 irradiation also resulted in increase of gate oxide leakage current. However, the drain to source breakdown (BVds) did not exhibit any obvious degradation by Co-60 irradiation up to a radiation dose of 200 kGy. The radiation damaged power DMOSFETs can be efficiently recovered by forming gas annealing at 400℃. Presumably, the radiation induced broken bonds in the damaged gate oxide were healed by hydrogen reaction during the forming gas annealing, resulting in the recovery of gate oxide quality (recovery of Ig-Vg characteristic) as well as substantial decrease in radiation induced oxide charges. However, it is found that the forming gas annealing was not able to anneal out the radiation induced interface traps. Since the threshold voltage shift arisen from Co-60 irradiation is mainly due to radiation induced positive oxide charge, the threshold voltage of the power MOSFETs can be efficiently recovered by the forming gas annealing at 400℃. Thermal annealing in pure N2 ambient also exhibited restorative ability for the radiation damaged devices, but to a much less extent.