A Spectroscopic SEM: First Results

Using a circular beam separator to deflect the primary beam of an SEM through 90deg, an aberration limited final probe size of 7-8 nm has been achieved in experiments. This limit was shown to be due to magnetic leakage fields from the post-deflector lens and not due to aberrations of the beam separator. In fact, it is concluded that the beam separator aberrations are within 2 nm over a 1 mum by 1 mum field-of-view, in agreement with previous simulation predictions. The results presented in this paper therefore confirm the feasibility of the spectroscopic SEM concept, from the imaging point of view, the next step is to acquire energy spectra. To further improve on the current setup, it is clear that a post-deflector lens without significant magnetic leakage field must be used. In addition, the lens should not be a transmission type as the SPSSEM relies on scattered electrons travelling back towards the beam separator. Such a lens has been designed and manufactured and is an immersion magnetic lens design which will be useful not only for imaging but also for spectrum experiments in the future