edfas.org 7 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 28 NO. 3 In comparison, EBAC imaging of the same structure displayed a continuous conductive path without a clear indication of the defect’s spatial origin (Figs. 3d and e). EBIRCH thus provided unambiguous defect localization through resistance change contrast rather than simple current mapping. HIGH-OHMIC DEFECT LOCALIZATION A high-ohmic defect (~100 MΩ) was identified in a viachain structure from a 10 nm processor (Fig. 5a). Leakage measurements showed diode-like I–V behavior with 10 to 100 nA leakage currents at ±1 V. The sample was biased at −1.2 V resulting in an approx. EBIRCH current of 1.5 µA through the defect, with an electron beam energy of 2 kV and beam current of 500 pA (Fig. 5b). Despite the low leakage, due to the diode-like nonlinear behavior of the defect (similar to other case studies), EBIRCH successfully detected resistance modulation down to sub-nanoamp levels, confirming its capability for high-impedance and nonlinear failure analysis (Fig. 5c). Even when the EBIRCH current was reduced to 300 pA, the defect spot remained visible, although the background signal from the underlying active area became noticeable at very high amplifier gains (Fig. 5d). Care was taken to avoid direct irradiation of active p–n junctions, which would otherwise generate strong EBIC signals and obscure the EBIRCH contrast. ADVANTAGES AND LIMITATIONS The principal advantage of EBIRCH is its direct sensitivity to local resistance variations, enabling defect localization over a wide resistance range without relying on absorbed-current contrast. By operating under an applied electrical bias, EBIRCH exploits electron-beaminduced perturbations, most notably localized heating, to modulate resistance and generate spatial contrast. This makes the technique particularly effective for identifying subtle low-ohmic and intermediate-ohmic defects that are difficult to resolve using conventional current-mapping approaches. At the same time, the electron beam plays a dual role in EBIRCH measurements. While it is essential for generating resistance contrast, beam-induced effects such as localized heating, charge trapping, or carrier redistribution may also modify the electrical response of the device under test. Under carefully controlled conditions, these interactions can enhance contrast and improve defect visibility, effectively increasing sensitivity to small resistance variations. Conversely, excessive beam energy, dose, or prolonged exposure may alter the defect state or surrounding material, leading to signal drift, contrast inversion, or changes in the apparent resistance. Fig. 3 Short in an SRAM of a 22 nm technology-node device. (a) SEM image showing the probe tips placed on the source and gate, respectively. (b) Raw EBIRCH image. (c) Overlay EBIRCH/SEM image highlighting the EBIRCH hotspot (red spot) (a filter showing the maximum current was applied by the EBIC overlay tool). (d) SEM image corresponding to (e) the EBAC signal. Note that the EBAC contrast indicates the presence of a short but does not provide the precise defect location. The scale bar represents 500 nm. (a) (b) (c) (d) (e)
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