On-axis Transmission Kikuchi Diffraction for Orientation Mapping of Nanocrystalline Materials in the SEM

Abstract

Electron Backscatter Diffraction (EBSD) in the SEM is routinely and widely used to produce local orientation maps of the microstructure of materials, via the automated recording and analysis of Kikuchi diffraction patterns. Orientation maps can then be easily processed to extract the following information: phase distribution, grain size distribution, orientation of individual grains, disorientation inside grains and grain boundary characterization. EBSD is thus overall a very powerful technique.One of the limits of EBSD though is its lateral resolution. Indeed, with a lateral resolution of about 50 nm [1], many features remain out of reach. Precisely with the objective of overcoming this limitation, a new diffraction technique was recently developed in the SEM, referred to as TKD or t-EBSD [2]. TKD (Transmission Kikuchi Diffraction) makes use of the same hardware as EBSD. The difference is that TKD uses electron transparent samples, prepared the same way as for TEM, instead of polished-bulk materials as for EBSD. The Kikuchi diffraction patterns in TKD are thus produced by the electron transmitted through the thin sample, instead of by the backscattered ones as for EBSD. It leads to a reduction of interaction volume and consequently an improvement in lateral resolution, from about 50 nm for EBSD to less than 10 nm for TKD [3][4][5].Following the recent developments of TKD, an even newer configuration was developed at LEM3: onaxis TKD [6]. This technique does involve a hardware modification in comparison to the conventional off-axis TKD first proposed by Keller and Geiss [2]. The scintillator is moved from its vertical position to a horizontal position under the transparent sample. The scintillator thus sits in the direction of highest transmitted intensity, enabling much faster acquisition speeds. It was previously estimated that on-axis TKD is 20 times faster than conventional TKD [7]. With a faster acquisition speed, on-axis TKD will be more suitable than conventional TKD for the analysis of beam sensitive materials. It also makes on-axis TKD less prone to beam drifts and instabilities.In term of lateral resolution, on-axis TKD falls seemingly in the same range as off-axis TKD (i.e. below 10 nm). However, the strength of on-axis TKD is that even the thinnest samples are exploitable (below 50 nm), which is where the interaction volume will be the smallest and consequently the resolution the best. This should give the edge to on-axis TKD in term of lateral resolution. Indeed, with very thin samples, most of the transmitted intensity is confined to a small angular range, especially with low-Z materials. The consequence is that little signal reaches the detector of the conventional configuration [3,4], while the on-axis detector beneficiates from an intense signal. A comparison between the two techniques remains to be done. In the meantime, the map displayed in figure 1 shows that grains as small as 10 nm are perfectly resolved with on-axis TKD, in particular in the top part of the map, where the sample is the thi...

T- SEM: Quantitative Composition and Structure Analysis of FIB lamellae in SEM

“…In another T-SEM experiment, SEM EDS and transmission Kikuchi diffraction (TKD) in SEM were combined to understand the element composition and crystallographic properties of Cu interconnects in Si-based semiconductor nanostructures. We show that achieving useful results on the nanometer scale in a suitable amount of time, is possible in SEM by combining on-axis TKD [1] with an annular EDS detector [2] and specimen preparation of electron transparent specimens by FIB.…”

Combined chemical and structural analysis of low dimensional systems in FEG-SEM

“…As shown in figure 1, TKD and EDS signals are simultaneously collected by both detectors. Since the OPTIMUS TKD detector and the specimen are aligned with the primary e-beam "on-axis" [4], TKD patterns are collected with minimal band distortions and fast measurement speeds at low probe currents. Since the Boersch effect is minimized, higher spatial resolution can be achieved.…”