Top-down topography of deeply etched silicon in the scanning electron microscope

The cross-sections of steep-sided etched lines and deep surface topography on partially completed integrated circuit wafers were measured. This was done using backscattered electrons (BSE) or low-loss electron (LLE) image in scanning electron microscope (SEM). The images contained regions where the collected signal was found zero due to the absence of direct line of sight between landing point of electron beam on the specimen and and the BSE or LLE detector. The surface topography can be measured by using the boundary of such a region in the SEM image as geometrical line.