edfas.org 9 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 28 NO. 2 have dimensions of 1.2 mm × 1.2 mm, and the applied spring‑pin force ensures reliable positioning of the sample on the printed circuit board (PCB) carrier without the use of adhesive, allowing for straightforward mounting and removal. The right panel of Fig. 5 shows an optical image of the region of interest, illustrating the connection between the electrodes and the probe pads. Each electrode has a length of 8 mm, corresponding to an estimated total parasitic resistance of approximately 128 Ω for two electrodes in the measurement circuit. High‑resolution OBIRCH analysis was performed using the oil‑immersion measurement configuration shown in Fig. 2b. Figure 6a shows a pattern image of the scanned nanoTSV chain, while Fig. 6b presents the measured OBIRCH signal. The high imaging resolution enabled accurate localization of the defect. A transmission electron microscopy (TEM) image of a localized defect using this method is shown in Fig. 6c. The root cause of the observed leakage failures was identified as partial filling of the nanoTSVs, leading to a lowering of the backside metal layer and resulting in a direct short to the substrate. CONCLUSION A novel approach is introduced that expands the applicability of optical‑microscopy‑based FA techniques, including LICA and OBIRCH, to increasingly downscaled device structures. It overcomes the working‑distance limitations of high‑NA objectives when probing and imaging must be performed from the same side of the chip. Two fabrication methods—stencil‑based metal transfer and metal inkjet printing—were developed to realize on‑chip extension electrodes. While the stencil‑based approach offers simplicity and rapid implementation, the inkjet‑printing method enables finer feature sizes and increased layout flexibility. The methodology was successfully demonstrated through the localization of a leakage failure in a fine‑pitch nanoTSV chain. (a) (b) (c) Fig. 5 Left, photograph of the test chip with inkjet‑printed electrodes mounted on a PCB carrier. Electrical contact to the inkjet‑printed probe pads is achieved using spring pins. Right, optical micrograph illustrating the connection between the electrodes and the probe pads. Fig. 6 Application of high‑resolution OBIRCH to a leaky nanoTSV chain: (a) pattern image (field of view: 10 µm × 10 µm); (b) corresponding OBIRCH image; and (c) TEM cross‑section at a defective area identified by OBIRCH.
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