The secondary electron signals of scanning electron microscopes (SEMs) are widely used in electron beam measurement systems in IC factories, since they reflect step-edge information of minute patterns. A theoretical approach to define the relationship of actual pattern edges and peaks of the secondary electron signal is necessary because of the difficulty of experimental determination.
Currently, a modified diffusion model is employed to predict the secondary electron signal distribution at edges; however, its direct application for steep edges presents some problems. A cylindrical projection model is therefore proposed for both steep and gentle edges, in which the secondary electron emission area is defined by the surface included by a cylinder rather than the spheroids of conventional models.
To establish the validity of the model, micro-edges were fabricated on silicon chips, and then evaluated by a metrological scanning electron microscope. Comparison of experimental and simulated results confirmed that the model predicted both peak position and edge gradient difference with good accuracy.