ANALYTICAL DESCRIPTION OF BACKSCATTERED ELECTRON SIGNAL FOR HIGH-RESOLUTION METROLOGY

Backscattered electron (BE) signals obtained by scanning fine features with a focused electron beam were studied. A commercial electron beam lithography machine (EBMF10 of Leica Cambridge) equipped with a channel plate detector was exploited for this purpose. The collected signal profile, and in particular the effect of the electron emission from the sidewalls of the feature under inspection (sidewall electrons, SWE) were studied. The variables we investigated include feature material and beam accelerating voltage. The effect of SWE on the BE signal was clarified by making use of Monte Carlo simulations. In particular it was possible to separate the SWE contribution from the global BE signal. Further, a novel analytical representation of the BE signal including the SWE effect was implemented. By this method, a precise linewidth measurement routine was developed and applied for metrology at different voltages on fine metal features of different materials. The application of this method to the metrology of submicron features (down to 0.2 mum) showed an intrinsic accuracy of better than 5% of the actual linewidth value.