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European Microscopy Congress 2020 Abstract Database

Challenges in Electron Beam-Induced Current Imaging: from SEM-EBIC to STEM-SEEBIC

Challenges in Electron Beam-Induced Current Imaging: from SEM-EBIC to STEM-SEEBIC

Session

PST.3 - New Instrumentation

Authors

Oscar Recalde (2), Alexander Zintler (2), Robert Eilhardt (2), Andreas Rummel (1), Leopoldo Molina-Luna (2)

Affiliations

1. Kleindiek Nanotechnik
2. TU Darmstadt

Keywords

MEMS-based device, SEM-EBIC, STEM-SEEBIC

Abstract text

Summary: A dedicated Electron Beam-Induced Current (EBIC) system, implemented in a Scanning Electron Microscope (SEM) has been used for the analysis of absorbed current related applications. Moreover, the employment of this EBIC system in a Scanning Transmission Electron Microscope (STEM) for controlled electric-field studies of semiconductor devices and the acquisition of high-resolution images using the Secondary-Electron-EBIC (SEEBIC) method has also been implemented.    

Introduction: EBIC has been extensively used for analysing semiconductors since many years, specifically due to the large information that can be acquired in terms of structure-property correlation for photovoltaic applications [1]. Furthermore, EBIC has also been used industrially as a failure analysis technique for hidden metallic networks, where the high energy absorption of metals induced by an incident electron beam generates a current along the network that can be directly detected by an EBIC system [2]. However, the study of materials using EBIC at higher magnifications, in STEM for instance, has been limited by inadequate electrical sample contacting and the poor current detection limit of amplifiers. Nowadays, the use of Focused Ion Beam (FIB) dual beam systems together with Micro Electrical Mechanical Systems (MEMS) for in situ STEM experiments allows suitable electrical connectivity of TEM lamellas at the nanoscale [3]. Additionally, the improvement of Transimpedance Amplifiers (TIA) technology has boosted the use of EBIC, from very high to low ohmic systems for a wide range of materials. In this regard, a deep understanding of signal acquisition induced by an incident electron beam at the SEM and STEM level could lead to a novel and powerful microscopy technique. Besides the conventional use of EBIC, for electric-field and absorbed energy applications, EBIC has proved to work as a perfect secondary electron detector, generating atomic resolution images comparable with the ones attained by the use of standard Angular Dark Field (ADF) detectors in STEM mode. This method is known as Secondary Electron EBIC (SEEBIC) [4] and is a technique that is able to collect the full information of holes generated by the production of secondary electrons and therefore, a high-resolution image of a specimen can be obtained [5].      

Methods/Materials: MEMS-based devices have been analysed under the bombardment of an incident electron beam at the SEM level. In the same way, a connectivity study of TEM lamellas for in situ STEM experiments prepared by FIB was also performed in oxide devices. Montecarlo simulations of electron scattering were performed by CASINO 3D software. In STEM, an analysis of the electric field in n-i-p junctions of Perovskite solar cells (PSCs) was carried on, as well as the application of the SEEBIC technique in single-ended TEM lamellas of oxide devices and gold nanoparticles. All the EBIC measurements were done by using a dedicated Kleindiek TIA.         

Results and Discussion: Hotspots of absorbed energy and charged zones of different materials has been visualized and measured along with a MEMS-based device on an SEM-FIB. The relationship of the EBIC signal, material property, and incident electron beam energy fits with the Montecarlo simulations performed in CASINO 3D software, showing the tendency of materials to absorbed energy based on the penetration depth of the electron beam. It has been proved, the use of an EBIC system as an electrical conductivity pre-test method for TEM lamellas by visualization of electrically current paths along with the specimen connected on a MEMS-based device. On the other hand, by using STEM-EBIC it was possible to visualize the current induced by electron-hole pair production on a n-i-p junction of a PSCs material, showing preferential current paths within the device.  Finally, we acquired STEM-SEEBIC high-resolution images of single-ended lamellas of oxide devices and gold nanoparticles deposited on the MEMS-based device.        

Conclusion: The use of an EBIC system together with MEMS-based devices has shown to be a powerful technique from SEM to STEM level. The study of the electric-field, absorbed energy and even as a SE electron detector for the acquisition of atomic resolution images shows the great variety of studies that can be performed by using an EBIC system. Nevertheless, the identification of electrical current signals in SEM studies and the improvement of image quality and noise reduction in STEM are still major problems to be resolved.

References

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[5]        M. Mecklenburg, W. A. Hubbard, J. J. Lodico, and B. C. Regan, “Electron beam-induced current imaging with two-angstrom resolution,” Ultramicroscopy, p. 112852, Oct. 2019, doi: 10.1016/j.ultramic.2019.112852.