Effect of low-energy electron irradiation on voltage-capacity curves of Al/SiO2/Si structure

Charging of dielectric targets by electron irradiation is a well-known phenomenon which should be taken into account in characterization of dielectric materials and coatings with electron microscopy, in electron beam lithography, in development of dielectric coatings for spacecrafts and other fields of science and engineering. Charging kinetics is strongly affected by spatial distribution of electrons and holes formed by irradiation. At the experimental electron beam energy electron penetration depth is smaller than dielectric thickness and this allows identifying the contribution of excess carrier transport to trap formation at the SiO2/Si interface. Low-energy electron beams have been shown to substantially affect C–V curve slope, i.e., to form traps at the interface. We have studied the effect of bias applied to the test structure before and after electron beam irradiation. The experiment has shown that bias of either polarity applied to the test MOS structure before low-energy electron beam irradiation practically does not affect the C–V curves of the test structure. Positive bias applied to the metallization layer during low-energy electron beam irradiation has a strong effect on the C–V curve pattern while negative bias affects the C–V curves but slightly. Study of the stability of the changes caused by electron beam irradiation has shown that the C–V curves of the test structure restore slowly even at room temperature. Application of negative bias decelerated charge relaxation.