Local Field of Surface and Redistribution Properties of Secondary Electrons Emitted from Insulating Thin Film with Negative Charge
绝缘膜负带电时的表面局部电场与二次电子返回特性

To investigate the principle of imaging for the marker below an insulating thin film charged weak-negatively with a scanning electron microscope (SEM) in the updated integrated circuit overlay measurement,a Monte Carlo simulation of electron scattering in the insulating thin film is performed first.The Mott cross section and modified Bethe formula are used for calculating elastic and inelastic scattering processes,respectively.The potential profile of the local field near the irradiating area is then calculated from the spatial distribution of holes and electrons.Trajectories of secondary electrons (SE) emitted from the film surface are numerically simulated,and the SE signal current that produces the SEM image contrast is obtained.It is shown that the SE signal current decreases with surface potential,which is in good agreement with the experimental variation of the SEM image brightness with irradiating time.