Radiation damage and its effect on hot-carrier induced instability of 0.5 μm CMOS devices patterned using synchrotron x-ray lithography

Abstract

The device characteristics and the radiation damgae 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. In addition to neutral traps, large amounts of positive oxide charge and interface states, particularly acceptor-like interface states, which cause degradation of MOSFET characteristics are found to be 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 damage on hot electron induced instability is found to be more severe in n +-poly buried-channel p-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. These results suggest that the major degradation mechanism due to hot-carrier in p-channel MOSFETs is electron trapping and in n-channel MOSFETs is interface state generation. It also suggests that p-channel MOSFETs, in addition to n-channel MOSFETs, needs to be carefully examined in terms of hot carrier induced instability in CMOS VLSI circuits patterned using x-ray lithography. © 1990 The Mineral, Metal & Materials Society, Inc.