Analysis of Effective Gate Length Modulation by X-Ray Irradiation for Fully Depleted SOI p-MOSFETs

An X-ray irradiation degradation mechanism has been investigated for fully depleted-silicon-on-insulator (FD-SOI) p-channel MOSFETs (p-MOSFETs). It is found that the drain current degradation by the X-ray irradiation has gate length dependence showing 20% degradation for L = 0.2 μm, while 8% for L = 10 μm after the 1.4 kGy(Si) X-ray irradiation. Using Terada's method, it was found that the degradation is not due to mobility degradation but due to radiation-induced gate length modulation (RIGLEM) and the associated increase of source and drain parasitic resistance. The major cause of degradation induced by the RIGLEM is explained by an analytical model, assuming a positive charge generation in sidewall spacers. It can be suggested that the X-ray irradiation degradation of FD-SOI p-MOSFET can be improved by optimizing the lightly doped drain region.