Mapping Chemical Bonds in Semiconductor Devices by Monitoring the Shifts of EELS Edges

Abstract

Scanning transmission electron microscopy (STEM) in combination with electron energy-loss spectroscopy (EELS) can deliver information about variations of bonding at the nm scale. This is typically performed by analyzing the electron-loss near edge structure (ELNES) of given EELS edges. The present paper demonstrates an alternative way of a bonding examination through monitoring the EELS onset positions. Two conditions are essential for their accurate measurement. One (hardware) is using the dual EELS instrumentation that provides near simultaneous acquisition of low-loss and core-loss spectra. Another (software) is the least-square fitting of observed spectra to a reference spectrum. The combination of these hardware and software techniques reveals the positions of EELS onsets with the precision sufficient for mapping tiny variations of bonding. The paper shows that the method is capable of helping to solve practical tasks of nanoscale engineering like the analysis of modern CMOS devices.

STEM Tools for Semiconductor Characterization: Beyond High-Resolution Imaging

“…The exact amount of energy lost by the electrons irradiating the sample is characteristic of the atomic species constituting the material, providing an accurate analytical tool. Indeed, EELS capabilities are far beyond compositional analyses, as the energy onset and fine structure of the ionization edges (i.e., the shape of the spectral peak) contain information on the oxidation state, local coordination [ 50 ], or bonding configuration [ 51 ].…”

Correlative STEM-HAADF and STEM-EDX tomography for the 3D morphological and chemical analysis of semiconductor devices

“…STEM-EDX mode is currently more used than STEM-EELS for the 3D structural and compositional analysis of semiconductor devices, most likely due to the simplicity of the experimental setup and the multi-frame acquisition scheme readily implemented in modern analytical TEMs. STEM-EELS remains, however, a powerful technique used in 2D for elemental mapping of light elements [2,17] and investigation of oxidation states and chemical bonds by energy loss near edge structure analysis [18]. In this work, we chose the STEM-EDX mode for the 3D elemental analysis but note that a similar experiment was conducted using STEM-EELS [19], and simultaneous STEM-EELS/EDX experiments are possible in modern analytical TEMs.…”