The charging effect of an insulating specimen from electron beam (e-beam) irradiation may be utilized to facilitate imaging in the scanning electron microscope (SEM). This has been confirmed by a great deal of experimental work during the last three decades. Particularly, recent investigations indicate that even located underneath insulating thin films that a low energy e-beam cannot penetrate, conductors not biased and overlay marks, are observable through a novel imaging pattern, charging contrast. Unlike conventional SEM contrasts, which usually reflect surface characteristics, the dynamic charging contrast can reveal information of underlying structures without any external exciting signal. The authors consider that this kind of charging contrast arises from the different redistribution rates of secondary electrons returning to the surface under the surface local field of the charged specimen. The charging contrast has the prospect of extending the SEM application and forming new testing methods matched with the fast development of integrated circuits.

No abstract