It was found that radiation induced flatband voltage shift of MOS capacitors with positive gate bias is proportional to the third power of the SiO2 thickness. The experimental results indicate that radiation induced interface states play an important role in flatband voltage shift of MOS capacitors. It was discovered that in view of radiation hardness

1000℃ is the best temperature for dry oxidation and that annealing at temperature above 1000℃ or hydrogen atoms coming into the Si-SiO2 interface will seriously degrade the radiation tolerance of MOS devices. It was supposed that radiation induced interface states mainly result from the existence of unionized excess silicon atoms in the Si-SiO2 transition layer.