Reducing curtaining effects in FIB/SEM applications by a goniometer stage and an image processing method

Abstract

In the last two decades, focused ion beam (FIB) systems have been used for sample preparation. For example, the edges of a sample can be polished for analytical measurements or continuous cross-sections can be milled for three-dimensional (3D) tomography and reconstruction. One major challenge in both procedures is the so-called curtaining effect, i.e., increasing surface roughness in the direction of the milling depth. The roughness of the cut can influence the result of the measurement and the segmentation process. In the present study, the authors report on two different methods to reduce the curtaining effect, namely, a hardware- and a software-based solution. For instance, Tescan implemented the so-called “rocking stage” in its plasma FIB. However, this is not available for other FIB systems. Therefore, for our FEI gallium FIB, an inhouse-developed goniometer stage is installed, which can be adapted as necessary. With this relatively inexpensive solution, the sample can be rotated around an additional axis and tilted by ±8°. Different sample heights are adjustable, and the sample's edge can be polished and imaged without stage movement. However, for automated milling and imaging procedures such as 3D tomography, such a tilting stage is not feasible. Therefore, as a second option, an image processing method is proposed that can be applied after the milling procedure on a whole image stack. A novel variation of this method for mathematical image processing is developed to reduce milling artifacts. Besides the curtaining effect, additional artifacts such as discontinuities caused by redeposition of previously removed materials or charging effects can be removed. The method is applied to the entire 3D dataset, and distortions are reduced by using information of their particular structure and directional dependence. The resulting new image stack can then be used to compose a 3D volume reconstruction. As an example, the geometries of silicon carbide particles reinforcing an aluminum matrix can be measured with nearly no milling artifacts.

Ellipsoidal mesoscale mineralization pattern in human cortical bone revealed in 3D by plasma focused ion beam serial sectioning

“…Imaging was completed with a retractable concentric backscattered detector (CBS). Sequential milling and images were collected using automated Slice and View software (Thermo Scientific, OR, USA), with a 4 nA ion current, 30 keV accelerating voltage, 20 nm slice thickness, and a 4° stage rocking angle, which has been demonstrated to minimize curtaining artifacts (Loeber et al, 2017). A full workflow is visualized in Figure S3.…”

Working Principle of an Ionic Liquid Interlayer During Pressureless Lithium Stripping on Li6.25Al0.25La3Zr2O12 (LLZO) Garnet‐Type Solid Electrolyte

“…Otherwise, some vertical lines are visible. This “curtaining” is known in literature and frequently happens when performing FIB cuts and is therefore not to be attributed to the samples morphology [56–58] …”

Image Segmentation for FIB-SEM Serial Sectioning of a Si/C–Graphite Composite Anode Microstructure Based on Preprocessing and Global Thresholding

“…The fourth issue is related to the occurrence of vertical stripes with rapid contrast changes, called curtain artifacts, which are shown as arrows in Figure 1b. This is attributed to the differences in the local milling rates due to the locally varying material characteristics of multiphase structures or porous materials (Denisyuk et al, 2017; Fitschen et al, 2017), ion channeling for (poly)crystalline materials (Giannuzzi, 2004; Volkert & Minor, 2007), and/or under-dose of ion beam (Loeber et al, 2017). Despite the presence of the platinum protection layer on the specimen, curtain artifacts can be observed in FIB-SEM images (Giannuzzi, 2004; Loeber et al, 2017).…”

“…Therefore, a number of studies, both hardware- and software-based, have been conducted to reduce the curtain artifacts. In the hardware-based approaches, the curtain artifacts can be reduced by applying a thick and uniform protective layer (Giannuzzi, 2004) and using a rocking stage to tilt the direction of ion beam onto the sample (Loeber et al, 2017), etc. The software-based approaches include the variational optimization-based approach (Fitschen et al, 2017), the wavelet transform-based approach (Münch et al, 2009), and the Fourier transform-based approach (Sosa et al, 2014).…”