edfas.org 7 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 25 NO. 4 for many analytic purposes. Several have been installed at synchrotron beamlines for diverse energy bands and scientific goals.[11] They are also used for analysis of radioactive materials in the nuclear fuel cycle[12] and to study the decay-energy spectrum of isotopes such as 163Ho that are sensitive to the mass of the electron neutrino. TES spectrometers are planned for multiple orbiting x-ray telescopes and will analyze samples returned from an asteroid. TES arrays are also excellent tools for the analysis of more usual, earth-bound materials. In one recent example, we used the emission spectra of several lanthanide-series elements to improve our understanding of certain x-ray fundamental parameters, including the energies and line shapes[13] and relative intensities[14] of the elements’ L-series emission lines (Fig. 4). While TESs do not directly register photon energies, energy calibration to one part in 104 is possible if enough reference materials—such as the 3d transition metals—are measured along with the unknown samples. The sensitivity and high resolution of the TES also enables the discrimination of distinct chemical states, such as Ka and Kβ emission of titanium (Fig. 5).[15] X-RAY NANO-CT DEMONSTRATED WITH TES ARRAYS The energy resolution of a TES spectrometer can also serve as a powerful tool to distinguish signal photons from backgrounds. A new research instrument called the tomographic circuit analysis tool (Tomcat) is the first to use this property of TESs in an x-ray computed tomography (CT) measurement. It recently imaged a small region of an IC and resolved wiring features as small as 160 nm.[16] In future research, the spectrometer will also be able to analyze the elemental composition of the sample, taking advantage of the element-dependent nature of x-ray transmission as a function of energy. The Tomcat instrument uses the tiny electron beam of a SEM to generate a concentrated source of x-rays for a measurement of x-ray transmission through the IC sample (Fig. 1). The SEM focuses electrons to a spot approximately 100 nm in diameter while accelerating them with a 25 kV potential. A thin-film target, 100 nm of platinum, converts many of the electrons to x-ray photons. The conversion happens in two ways: through broadband Fig. 4 Emission spectra of two lanthanide-series metals, a demonstration of the energy resolution and the wide range of energies and intensities the TES can measure.[13] For clarity, the holmium spectrum is scaled up by a factor of 1000. Fig. 5 TES-measured Kɑ and Kβ emission spectra of titanium in various oxidation states.
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