Abstract
The magnitudes of the challenges facing electron-based metrology for post-CMOS technology are reviewed. Directed selfassembly, nanophotonics/plasmonics, and resistive switches and selectors, are examined as exemplars of important post-CMOS technologies. Materials, devices, and architectures emerging from these technologies pose new metrology requirements: defect detection, possibly subsurface, in soft materials, accurate measurement of size, shape, and roughness of structures for nanophotonic devices, contamination-free measurement of surface-sensitive structures, and identification of subtle structural, chemical, or electronic changes of state associated with switching in non-volatile memory elements. Electron-beam techniques are examined in the light of these emerging requirements. The strong electron-matter interaction provides measurable signal from small sample features, rendering electron-beam methods more suitable than most for nanometer-scale metrology, but as is to be expected, solutions to many of the measurement challenges are yet to be demonstrated. The seeds of possible solutions are identified when they are available.
Highlights
Electron-beam-based metrology is indispensable in the manufacture of integrated circuits (ICs) and drives progress in instrumentation and data analysis.[1]
A wide range of techniques, including electron energy-loss spectroscopy (EELS),[68,77] Auger electron spectroscopy (AES),[77] energy-dispersive x-ray spectroscopy (EDX),[78] and electron holography,[71] in addition to Bragg contrast[76,79] have all been employed, sometimes leading to conflicting results between studies—a problem likely caused by both significant experimental differences and the relatively weak signals produced by the often subtle material changes.[66]
Very strong contrast has been observed in electron beam-induced current (EBIC) observations of these systems with low energy electrons,[80] and recent studies have provided new insights into the complex image formation processes involved.[81,82]
Summary
Electron-beam-based metrology is indispensable in the manufacture of integrated circuits (ICs) and drives progress in instrumentation and data analysis.[1]. Two-dimensional materials, such as graphene, hexagonal boron nitride, and transition metal dichalcogenides (Mo and W with S, Se, and Te), are an obvious class, but similar considerations can apply to many nanoscale structures, where surface-to-volume ratios are very large and the mobility of surface atoms is much higher than that in the bulk.[31,32] Understanding the behavior of these materials depends on knowing the configuration of single-atom defects and precise measurements of atomic positions, which in turn implies an ability to image such defects in a non-perturbative fashion This latter requirement is daunting since, under many standard imaging conditions, it is impossible to tell if the sample is in a pristine state. Accurate correlation between optical behavior and measured dimensions requires that the measurement method produces minimal contamination
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