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Electrical Isolation Preserved by Plasma Focused Ion Beam TEM Sample Preparation and Verified with STEM SEEBIC Imaging
Abstract
Electrical Isolation Preserved by Plasma Focused Ion Beam TEM Sample Preparation and Verified with STEM SEEBIC Imaging - Matthew Mecklenburg, Fred Shaapur, William Hubbard, Brian Zutter, B. C. Regan
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We report electronic transport mapping in a single dielectric layer of a polycrystalline BaTiO3 multilayer ceramic capacitor (MLCC) by electron beam induced current (EBIC) measurements using a scanning transmission electron microscope. Ga⁺ focused ion beam-lift out techniques with organometallic Pt-deposition are used to extract and electrically connect to these devices while maintaining high (>gigaohm) resistance between electrodes. Different modes of EBIC are observed depending on device resistivity. We demonstrate the use of EBIC resulting from secondary electron emission as a method for performing resistance contrast imaging (RCI), with resistive grain boundaries appearing as steps in EBIC contrast. These RCI maps are also used to calculate the potential and electric field of the device under an arbitrary bias. A mix of high- and low-resistance ohmic as well as rectifying grain boundaries is observed. These results help to better establish the distribution of resistivities critical to the prevention of performance-limiting current leakage in MLCCs.
One of the most important applications of a focused ion beam (FIB) workstation is preparing samples for transmission electron microscope (TEM) investigation. Samples must be uniformly thin to enable the analyzing beam of electrons to penetrate. The FIB enables not only the preparation of large, uniformly thick, sitespecific samples, but also the fabrication of lamellae used for TEM samples from composite samples consisting of inorganic and organic materials with very different properties. This article gives an overview of the variety of techniques that have been developed to prepare the final TEM specimen. The strengths of these methods as well as the problems, such as FIB-induced damage and Ga contamination, are illustrated with examples. Most recently, FIB-thinned lamellae were used to improve the spatial resolution of electron backscatter diffraction and energy-dispersive x-ray mapping. Examples are presented to illustrate the capabilities, difficulties, and future potential of FIB.
An electron microscope's primary beam simultaneously ejects secondary electrons (SEs) from the sample and generates electron beam-induced currents (EBICs) in the sample. Both signals can be captured and digitized to produce images. The off-sample Everhart-Thornley detectors that are common in scanning electron microscopes (SEMs) can detect SEs with low noise and high bandwidth. However, the transimpedance amplifiers appropriate for detecting EBICs do not have such good performance, which makes accessing the benefits of EBIC imaging at high-resolution relatively more challenging. Here we report lattice-resolution imaging via detection of the EBIC produced by SE emission (SEEBIC). We use an aberration-corrected scanning transmission electron microscope (STEM), and image both microfabricated devices and standard calibration grids.
Adjusting the STEM Sample Holder Potential for Improved EBIC Contrast - Volume 25 Supplement - Matthew Mecklenburg, William A. Hubbard, Ho Leung Chan, B. C. Regan
In standard electron-beam-induced-current (EBIC) imaging, the scanning electron beam creates electron-hole pairs that are separated by an in-sample electric field, producing a current in the sample. In standard scanning electron microscopy (SEM), the scanning electron beam ejects secondary electrons (SEs), which are detected away from the sample. While a beam electron in a scanning transmission electron microscope (STEM) can produce many electron-hole pairs, the yield of SEs is only a few percent for beam energies in the range 60–300 keV, making the latter signal much more difficult to detect on sample as an EBIC. Here we show that the on-sample EBIC in a STEM registers both SE emission and SE capture as holes and electrons, respectively. Detecting both charge carriers produces differential image contrast not accessible with standard, off-sample SE imaging. In a double EBIC-imaging configuration incorporating two current amplifiers, both charge carriers can even be captured simultaneously. Compared with the current produced in standard EBIC imaging, which highlights only the regions in a sample that contain electric fields, the EBIC produced by SE emission, or SEEBIC, is small (picoampere scale). But SEEBIC imaging can produce contrast anywhere in a sample, exposing the texture of buried interfaces, connectivity, and other electronic properties of interest in nanoelectronic devices, even in metals and other structures without internal electric fields.
Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.
- J Mayer
J Mayer et al., MRS BULLETIN 32 (2007), p. 400.
- Wa Hubbard
WA Hubbard et al., Physical Review Applied 10 (2018), p. 044066.
- M Mecklenburg
M Mecklenburg et al., Microscopy and Microanalysis 25 (S2) (2019), p. 2354-2355.
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- M Mecklenburg
M Mecklenburg et al., Microscopy and Microanalysis 19 (S2) (2013), p. 458-459.