Type of presentation: Poster

IT-4-P-2766 A novel SEM triple in-lens detection system

Wall D. C.¹, Vystavel T.², Tuma L.², Skalicky J.², Sasam F.¹, Wandrol P.²

¹FEI Company, Eindhoven, The Netherlands, ²FEI Company, Brno, Czech Republic

David.Wall@fei.com

The advent of new materials and new techniques in SEM and DualBeam has driven the need for better detection in recent years. Traditionally, in-lens detection systems have focussed on energy selection of signal, due to the small opening angle of signal that can be detected, while modern, below-lens detectors have the benefit of separating angular differences in signal. This has typically meant that the in-lens detection system has had strong benefits for resolving materials with fine difference in the composition, while below-the-lens has been more suited to channelling contrast.
In this abstract, a new type of electron column design is introduced which broadens the spectrum of BSE’s and SE’s that can be detected with the in-lens detectors. The newly introduced NICol SEM column positions the in-lens BSE detector at the lowest point of the column, so that the opening angle of BSE that can reach the detector is far higher than those typically positioned higher up. The benefit of this can be seen in the images of figure 1. where strong channelling contrast is now possible with in-lens detection. This enables the collection of strong grain orientation images even while tilted or in 3D data collection in DualBeam configurations, where previously below-lens detectors is more difficult to use due to possible collisions. Additionally, by segmenting the annular design of this BSE detector into left and right segments, two separate signals can be detected and processed. Adding these these segments delivers material or orientation contrast, while a differential image generates strong topographical contrast. Where topographical images are necessary on charging material, this technique can avoid the charge.

By fully utilizing the experiment geometry, clear separation between high and low energy secondary electrons can also be enabled with the further two in-lens detectors in the SEM. Very low energy, surface sensitive signal will be affected most by the electrostatic field and travels closest to the beam axis. Higher energy secondary electrons less affected by the electrostatic lens are projected onto the middle detector. These effects can be seen in Fig. 2 (a, b) where the lower energy SE image shows excellent surface information while the higher energy SE image shows the best edge contrast. This signal can then be detected on the upper detector. Simultaneous collection of all three of these signals enables the collection of all information in a single scan, reducing charge up effects, and preventing beam damage or contamination to the sample.

Fig. 1: SEM image of FIB cross-section through steel sample acquired at 1.8 keV exhibiting strong channeling contrast. This enables clear identification of austenite and ferrite regions.	Fig. 2: Simultaneous SEM images acquired using high energy (left) and low energy (right) secondary electrons using a primary beam energy of 2kV revealing edge and surface sensitivity.
Fig. 3: Simultaneous SEM images acquired using high energy (left) and low energy (right) secondary electrons using a primary beam energy of 2kV revealing edge and surface sensitivity.