Chapter/Index: Introduction | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Appendix
| Electron Beam Absorbed Current (EBAC), also called Resistive Contrast Imaging (RCI), is based on a similar principle as Electron Beam Induced Current (EBIC). In this technique, the electron beam of SEM injects charges which is then absorbed by metal lines under the surface. Therefore, a current is induced and measured by a probe placed on the SEM sample. In this case, the probed signal is overlaid on the secondary electron image so that direct localization of the failure becomes possible. Note that EBAC is especially used to locate failures in metallization networks inside semiconductor devices. Figure 1263a shows that a strong EBAC signal is observed from an underlying active area when EBAC measurement is performed on a leaky gate.
Figure 1263a. EBAC Results of the bad sample. [1] Figure 1263b shows an open failure observed with an electron beam at 7 keV by Zyvex Nanoprobing system. The EBAC signal from both metal 5 and metal 4 are observable but electron beam penetration depth is not large enough to observe metal 3. The comparison between good and bad locations showed that there was a signal break on the failed unit which correlated exactly to a metal 5 – metal 4 connection via a single via 4 as shown in the zoom in layout snapshot in Figure 1263b (b). Subsequent FIB cross-section along AA' in Figure 1263b showed via bottom void confirming the suspected open defect.
Figure 1263c shows an EBAC test targeting a gate defect of CMOS image sensors. For two samples, S1 and S2, which are suspected to have damaged gates, the gate and source contacts are exposed and then a bias is applied. In images (a) and (c), acquired through conventional EBAC analysis, the entire component region is visible, making it difficult to pinpoint specific defect sites. Conversely, the DI-EBAC images (b) and (d) highlight localized response areas, with sizes ranging from 0.10 to 0.15 μm. The STEM image in Figure 1263c (f) shows the cross-sectional analysis results of the S1 sample region near the DI-EBAC reaction site. A short defect is observed between the W contact and the Si substrate. Electron-beam irradiation of short-circuit paths between various materials generates a thermoelectromotive force via the Seebeck effect, which is detected through current variations. This example confirms that DI-EBAC provides high resolution and serves as an effective tool for analyzing short defects.
Figure 1263d shows a DI-EABC image taken from an area with a metal short defect in a CMOS image sensor.
[1] Ping Khai Tan, M. K. Dawood, G. R. Low, H. H. Yap, Ruiyang He, Seung Je Moon, Hong Ying Feng, Hao Tan, Y. M. Huang, D. D. Wang, Y. Z. Zhao, Yongkai Zhou, S. James, C. Q. Chen, Jeffery Y.K. Lam, Z. H. Mai, Nanoprobing EBAC technique to reveal the failure root cause of gate oxide reliability issues of an IC process, 2014 IEEE International IntegratedReliability Workshop, DOI:10.1109/iirw.2014.7049496.
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