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ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 21 NO. 3 26 EDFAAO (2019) 3:26-32

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RECENT ADVANCES IN VLSI CHARACTERIZATION USING THE TEM Frieder H. Baumann Center for Complex Analysis, GlobalFoundries, Malta, New York frieder.baumann@globalfoundries.com

INTRODUCTION When building complex structures such as electronic devices on silicon wafers, image forming techniques are essential in debugging the process. Themain tool used to be the scanning electron microscope (SEM), which offers high throughput and fast turnaround at a resolution of just a few nanometers. With device dimensions shrinking below 50 nm, however, the role of imaging has slowly moved to the more complex transmission electron microscope (TEM) tool. Finally, with the advent of inherently 3D devices such as FinFETs at the 20 nm node, the TEM has begun to take over the role of the workhorse in the imaging realm. Parallel to its move into the mainstream, new tech- niques were developed, which transformed the TEM from a pure imaging tool into a versatile instrument for physi- cal and compositional characterization of the region of interest. In conjunctionwith precisely localized specimen preparation using focused ion beam techniques, failure analysis without a TEM has become almost unthinkable in modern semiconductor manufacturing. ENABLING INNOVATIONS Some key factors in the tremendous progress of the art of electronmicroscopy over the past two decades include the improvement of electron optics, refinement of spec- troscopic techniques, and introduction of the CCD camera for image and spectroscopy recording. Last but not least, theadvancement incomputingpower (at theTEMtool and offline) enables the analyst to use modern mathematical techniques for data analysis and noise reduction. In the area of electron optics, the introduction of lens correction systems—correcting the spherical aberration (Cs)—has pushed the spatial resolution far into the sub- 0.1 nm regime. Cs-corrected TEM tools are commercially

available from several vendors and are slowly but surely becoming the standard for high resolution imaging appli- cations. Even more important, although less obvious, was the introduction of the field emission gun (FEG) to mainstream tools. [1] Only the enormous brightness and superior coherence of the electrons emitted from an FEG allows imaging and electron spectroscopy at very high resolution, and even electron holography in the TEM for dopant mapping (Fig. 1). Using a CCD camera instead of photo plates dramati- cally decreases the turnaround time for TEM imaging and makes images instantly available. [1] In addition, the CCD camera with its linear response to the electron dose transformed the art of electronmicroscopy into a quanti- tative science, enabling electron energy loss spectroscopy

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Fig. 1 Important innovations in the TEM: (a) With the move to cold, sharp tips in the gun, the electron beam obtains laser-like coherence. (b) The CCD allows instant linear readout of images and spectra. (c) Multiple windowless x-ray detectors enable fast elemental mapping, even of light elements.

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