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(EELS), energy filtered imaging, electron crystallography, and much more. Further, the dramatic increase in com- puting power and data storage capacity enables researchers to runa fully automated, complete TEM session. [2] This allows for long and/or tedious data acquisition procedures to be performed without supervision, as will be described in the electron tomog- raphy section. One particular innovationof great impact for the failure analysis (FA) community was

ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 21 NO. 3

Fig. 2 X-ray map of a planar replacement gate, acquired in just a fewminutes in STEMmode. Each element is depicted in its own color (Si not plotted for clarity), thus the nickname “TEM color photography.”

the introduction of multiple, windowless x-ray detectors embedded into the TEM column for energy dispersive x-ray (EDX) spectroscopy. Several detectors in immediate proximity of the sample increase the solid angle for x-ray detection by an order ofmagnitude, and allowacquisition of x-ray maps in minutes instead of hours, even for light elements, with less radiation damage. This technology alsodelivers x-raymapping almost as fast as scanningTEM (STEM) imaging and has made “TEM color photography,” with one color for each element, a reality (Fig. 2). This article explores how recently introduced TEM characterization techniques can help the TEManalyst and FA community to understand and improve the processes and integration schemes. These techniques include pre- cession electron diffraction for grain and strain analysis, noise reduction processing for lowdose EELSmapping for

resulting diffraction pattern is still from the same area as in a nano-diffraction setting, but the pattern is free of dynamic scattering artifacts. Rather, it consists of more spots, which are all homogenously illuminated and easy toanalyze. The combinationof PEDwith fast data read-out of the diffraction patterns leads to high resolution strain or grain maps, as can be seen in Figs. 3 and 4. Figure 3a schematically depicts the principle of PED. The beam is rotated around the vertical axis (hollow cone illumination) and produces a large and mostly kinematic diffraction pattern, which can be easily analyzed. The high S/N ratio of the fitted diffraction patterns allows strain determination in the channel with a precision of better than 0.1%. Warmcolors in Fig. 3 represent enlarged lattice spacing, while cold colors indicate compressed lattice (continued on page 30)

ultra-low-k (ULK) materials, and EDX tomog- raphy for elemental 3D imaging of defects. PRECESSION ELECTRON DIFFRACTION Electrondiffraction in theTEMhas always been an essential tool for the analyst to obtain information from the sample. A dif- fraction pattern represents a 2D cut of the crystal lattice under examination. Therefore, distortion of the diffraction pattern is a sign of lattice strain, while the symmetry of the pattern points toward the sample orientation. Precession electron diffraction (PED) [3] is a special form of nano-beam diffraction: Using a small aperture, a narrow parallel beam is formed and a diffraction pattern is recorded. In addition, this nano-beam is precessed around the incoming direction by an angle of roughly 1° (see Fig. 3). The

Fig. 3 (a) Schematic of precession electron diffraction (PED). (b) Strain maps of SiGe source/drain areas embedded in a Si matrix. The high S/N ratio of PED allows strain mapping with nm resolution and 0.1% strain sensitivity. (a) (b)

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