Feature enhancement by non-uniform ion-milling for SEM of integrated circuits

Abstract

A variety of techniques has been developed to enhance the image contrast of EM specimens in both physical and biological sciences. In SEM of materials, feature enhancement is mainly based on augmentation of surface topography by non-uniform material removal from different structural elements and preferential erosion at adjoining interfaces. The enhanced surface topography, in turn, translates into better response to the probing beam resulting in higher image contrast.In cross-sectional imaging by SEM (XSEM) of ICs, feature enhancement has been carried out by chemical or mechanical, i.e., ion-milling, surface treatments. Ion-milling has been used to clean surfaces and to enhance their topography. The non-uniform material removal from the surface, in this case, merely relies on an inherent characteristic of the structural elements, i.e., their relative erosion rates during the ion-thinning. An additional factor, i.e., minimization of the “shadowing” effect by adjusting the orientation of ion incidence may also be used to elevate the non-uniform ion-milling even further.