Experiment and simulation of charging effects in SEM

Abstract

In semiconductor manufacturing, control of hotspots by optical proximity correction (OPC) requires accurate measurements of shapes and sizes of fabricated features. These measurements are carried out using CD-SEM. In order to measure 2D shapes, edges of features should be clearly defined in all directions. Positions of edges are often unclear because of charging. Depending on the SEM setup and the pattern under measurement, the effect of charging varies. The influence of measurement conditions can be simulated and optimized. A Monte Carlo electron-beam simulation tool was developed, which takes into account electron scattering and charging. CD-SEM imaging of SiO₂ lines on Si were studied. In experiment, an effect of contrast tone reversal was found, when beam voltage was varied. The same effect was also found in simulations, where contrast reversal was similar to the experimental results. The time dependence of contrast variation was also studied. A good agreement between simulation and measurement was found. The simulation software proved reliable in predicting SEM images, which makes it an important tool to optimize settings of electron-beam tools. Based on such simulations, optimum conditions of SEM setup can be found.