Hot-carrier induced instability of 0.5 μm CMOS devices patterned using synchrotron X-ray lithography

The device characteristics and the radiation damage of n-channel and p-channel MOSFETs patterned using synchrotron X-ray lithography are examined. The effect of radiation damage caused by X-ray lithography on the device reliability during hot electron injection is investigated. Large amounts of positive oxide charge, neutral traps, and acceptor-like interface states are created by X-ray irradiation during the lithography process. Although several annealing steps are performed throughout the entire fabrication process, the radiation damage, particularly neutral traps, is not completely annealed out. The hot-electron-induced instability in p-channel MOSFETs is significantly increased due to the enhanced electron trapping in the oxide by residual traps. The effect of radiation on hot-electron-induced instability is found to be more severe in n⁺-poly buried-channel n-MOSFETs than in p⁺-poly surface-channel p-MOSFETs. However, the degradation in n-channel MOSFETs due to channel hot carriers is not significantly increased by X-ray lithography since the n-channel MOSFETs hot-carrier-induced degradation is dominated by interface state generation instead of electron trapping. These results suggest that p-channel MOSFETs, in addition to n-channel MOSFETs, need to be carefully examined in terms of hot-carrier-induced instability in CMOS VLSI circuits patterned using X-ray lithography.