USE OF MONTE-CARLO MODELING FOR INTERPRETING SCANNING ELECTRON-MICROSCOPE LINEWIDTH MEASUREMENTS

A scanning electron microscope (SEM) can be used to measure the dimens ions of the microlithographic features of integrated circuits. However , without a good model of the electron-beam/specimen interaction, accu rate edge location cannot be obtained. A Monte Carlo code has been dev eloped to model the interaction of an electron beam with one or two li nes lithographically produced on a multilayer substrate. The purpose o f the code is to enable one to extract the edge position of a line fro m SEM measurements. It is based on prior codes developed at the Nation al Institute of Standards and Technology, but with a new formulation f or the atomic scattering cross sections and the inclusion of a method to simulate edge roughness or rounding. The code is currently able to model the transmitted and backscattered electrons, and the results fro m the code have been applied to the analysis of electron transmission through gold lines on a thin silicon substrate, such as is used in an x-ray lithographic mask. Significant reductions in backscattering occu r because of the proximity of a neighboring line.