Large-Area High-Resolution Imaging

Challenge of High-Resolution SEM Imaging

Highest-resolution, accurate SEM imaging of “large samples” exceeding a single typical field of view (in the order of a few tens of μm) is a challenging procedure. A set of several hundreds or thousands of images have to be stitched together in order to display a surface spanning several millimeters or even centimeters as a “Google Earth”-style map. Any standard mechanical stage will have visible stitching errors, and thus yield distorted images.

The Raith systems are different: By reversing the functionality of a professional electron beam lithography tool, the sample surface is not exposed; instead, existing nanostructures are seamlessly imaged using the extreme placement accuracy of the tool infrastructure.

Users can benefit e. g. from the “on-board” Laser Interferometer Controlled Stage technology, related write field alignment functionality, and drift correction algorithms. These features deliver ultra-precise and fully automated image acquisition for generating highly accurate and undistorted “land maps” of large samples with highest resolution and stitching accuracy in the 10 nm range – and in 2D and in 3D in case several (sequentially deprocessed) layers are involved.

Reverse Engineering and Connectomics

Chip makers are not the only users to rely on Raith technology for reverse engineering applications and identification of counterfeiting or parasitic chips. Nanobiologists too, can use all these features to reveal the brain circuitry in connectomics. Here, analysis of the connectivity of neurons is the driver for (3D) brain mapping.

Large-area high-resolution mosaic image of an electrical device/chip. No software corrections have been applied; both the overview and the image zooms clearly show the difference in image stitching quality in comparison with a conventional SEM. Here, the stitching accuracy is of the order 10 nm. Green lines indicate the image overlap (~1μm) at the image acquisition boarders, which have intentionally been chosen to be very “generous”.

Image of the entire cross-section of a mouse spinal cord. This is the most accurate large-area high-resolution map of neuronal tissue directly acquired by an SEM instrument. This image contains 4.5*1010 pixels, whose locations are known to the high accuracy afforded by laser interferometry thus potentially supporting connectomics. By using the Laser Interferometer Stage and a calibrated 100 μm field of view, SEM images of a large-area of this mouse spinal cord can be accurately stitched together. These near perfect images were NOT processed for error correction.

Images: Christine A. Brantner, et al., George Washington University