Chemical mapping of semiconducting nanostructures (sub-10 nm) with large area windowless EDS/EDX detector in SEM

Session

Poster Session Three

Authors

Dr. Purvesh Soni (1)

Affiliations

1. Bruker Nano GmbH

Keywords

EDS, EDX, windowless, Semiconductor, FinFET, Spatial resolution, Chemical mapping, EDS map, SEM EDS, TEM EDS, EELS, STEM, 7 nm node technology, 14 nm node technology, qualitative analysis

Abstract text

As we approach the limits of semiconductor device miniaturization, the complexity of device design and the variety of materials used for enhancing the device performance also increases. The characterization of such complex structures is challenging since it requires careful specimen preparation. Typically, electron transparent specimens are being analyzed using transmission electron microscopes equipped with elemental analyzers such as energy dispersive X-ray spectroscopy (EDS/EDX) or electron energy loss spectroscopy (EELS).

This work presents the strength of EDS or EDX in SEM (as opposed to TEM) for chemical mapping and identification of complex nanostructures using bulk and electron-transparent specimens. Unlike APT and SIMS analysis, which requires specific specimen shape, size, and geometry; EDS mapping in SEM is a non-destructive technique used for large area-mapping with minimal sample preparation. It combines speed (measurement and data analysis), reliability, ease-of-use, and high spatial resolution. 

Commercially available CPUs with 7 nm and 14 nm node FinFET technology are investigated as bulk and e-transparent specimen with a 100mm2 oval shaped windowless EDS detector in FEG-SEM. 7 nm node technology FinFET devices exposed metal (M0) layers [1] are analyzed as bulk specimen by EDS at 3 kV, 5 kV and 20 kV. The EDS maps (Fig.1) show the elemental distribution of Co, Ge, Ti, Al, W, Si, Hf and O. Features smaller than 10 nm were resolved. Heavily overlapping x-ray lines from elements like Si, W and Hf were deconvoluted automatically. The respective element distribution in the specimen is presented in the elemental maps.

E-transparent specimens (FIB-lamella) prepared from 14 nm node technology FinFET devices [2] are used to obtain TEM-like results in SEM with EDS. The smaller interaction volume in e-transparent samples improves the EDS spatial resolution. However, the small ionization cross section (~ 25 nm in this case) on TEM-lamellae gives very low x-ray yields and thus lower x-ray fluorescence generation for EDS analysis as compared to bulk specimen. Features as small as 2-3 nm were chemically resolved on a ~25 nm thick FIB lamella.

These data show, that SEM EDS is a valuable tool for semiconductor analysis and can be a useful alternative to the complex and expensive TEM/STEM technology. 

References

[1] J.V. Oboňa, T. Hrnčíř, et al., Microsc. Microanal. 22 (Suppl 3), 2016, p56-57 

[2] A materials analysis study into FinFET technology, https://www.eag.com/app-note/a-materials-analysis-study-into-finfet-technology