AFM-in-SEM as a Tool for Comprehensive Sample Surface Analysis
Veronika Novotna,1 Josef Horak,1 *
josef.horak@nenovision.com
Abstract: Key features and applications of a unique atomic force microscope (AFM), the LiteScope™, which can be integrated into a scanning electron microscope (SEM) is reported. Using the AFM-in- SEM as one tool combines the capabilities of both systems in a very efficient way. The LiteScope design features advanced Correlative Probe and Electron Microscopy (CPEM)™ imaging technology that allows simultaneous acquisition of multiple AFM and SEM signals and their precise in-time correlation into a 3D CPEM view. AFM-in-SEM advantages are presented using several examples of applications and AFM measurement modes including CPEM, material electrical and mechanical properties together with nanoindentation, and focused ion beam (FIB) applications.
Keywords: atomic force microscopy, scanning electron microscopy, correlative microscopy, AFM-in-SEM, nanoindentation
Introduction A current trend in a surface investigation can be defined,
both in academia and industry, as follows: (i) the need to char- acterize and analyze structures in the (sub)nanometer range is growing; (ii) the complexity of such measurements across various instruments creates a demand for advanced correlative analysis; and (iii) easy-to-use instrumentation and automated procedures are of great interest. Atomic force microscopy (AFM) and scanning electron
microscopy (SEM) are two of the most used techniques for sample nanoscale analysis. To tackle market demands, Neno- Vision has developed a unique AFM, the LiteScope™, designed for integration into the SEM. Te motivation behind the design is twofold: first, such a hybrid system allows for efficient, yet complex in situ sample characterization, and, second, it brings new possibilities for advanced correlative imaging, which allows sample analysis in a way that was difficult or impossible by separate SEM and AFM systems. In SEM, the sample surface is scanned with a focused
primary electron beam [1]. Tis interaction produces various signals that, through a range of detectors, provide different information about the surface and its chemical composition [2]. In combination with focused ion beam (FIB), SEM is also used for surface modification. In general, a 2D SEM image pro- vides great material contrast and a large depth of focus [3], all in a wide range of imaging resolutions down to around 1 nm. On the other hand, an AFM scans the sample surface with
a sharp tip and measures attractive and repulsive forces emerg- ing between the tip and the sample [4]. Tanks to this prin- ciple, AFM can provide sub-nanometer resolution combined with information on topography, roughness, mechanical, and magnetic and electrical properties depending on the probe used. Tus, the integration of AFM inside a SEM combines the capabilities of both techniques and brings many advantages.
38 doi:10.1017/S1551929520000875 AFM-in-SEM integration enables true correlative imag-
ing where the region of interest (ROI) on the sample is ana- lyzed by AFM and SEM at the same time. Traditionally, the correlation is achieved by imaging the sample by a number of techniques, subsequently followed by data analysis and final image overlay, for example, correlative Raman imaging and scanning electron microscopy (RISE) is in this category [5]. Tere are also approaches for simultaneous measurements of multiple signals such as correlative light-electron micros- copy (CLEM) that combines an optical microscope with an SEM into one system [6]. Common issues with traditional approaches are either high initial investment into sophisti- cated, dedicated instruments or problematic image correlation due to data incompatibility (data formats, pixel count and size, etc.) between devices used [7]. LiteScope is equipped with Cor- relative Probe and Electron Microscopy (CPEM)™ technology that enables simultaneous data acquisition and correlation of multiple channels; for example, the material contrast given by SEM is merged with the 3D topography of surface features obtained by AFM, resulting in a 3D CPEM view (Figure 1). Another key advantage of the AFM-in-SEM approach is
in situ measurement, meaning minimal sample handling and contamination due to vacuum preservation inside the SEM, which is crucial for sensitive samples. Also, using SEM, the AFM tip can be navigated with nanometer precision to the ROI, which makes obtaining measurements extremely time- efficient and eliminates the need for navigation marks made by FIB milling. Lastly, the entire system is highly customizable (for exam-
ple, scanner configuration, immersion lens compatibility) and can be equipped with many additional accessories, such as a nanoindenter or tweezers, that further broadens possibilities of the AFM-in-SEM concept for complex and efficient sample analysis. Tis article demonstrates the abilities and advantages of
CPEM technology in AFM-in-SEM applications as well as use of the LiteScope as a stand-alone AFM. Technical aspects of the system, including self-sensing probes and supported mea- surement modes, are detailed in the Methods section. Te applications discussed cover a combination of key features and measurement modes including topography in combination with material, electrical, and mechanical properties and FIB milling applications.
Materials and Methods LiteScope is a compact AFM microscope (129 × 90 ×
45mm), designed to fit into the SEM chambers of most micro- scope manufacturers (TESCAN, Zeiss, TermoFisher Scientific,
www.microscopy-today.com • 2020 May Ondrej Novotny,1 Zdenek Novacek,1
* Martin Konecny,2 and Jan Neuman1
1NenoVision s.r.o., Purkynova 649/127, 61200, Brno, Czech Republic 2CEITEC BUT, Technicka 2896/2, 61600, Brno, Czech Republic
Veronika Hegrova,1
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