Electron microscopy
 
Electron Beam Absorbed Current (EBAC)/Resistive Contrast Imaging (RCI)
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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.

EBAC Results of the bad sample

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.

(a) EBAC analysis comparison between (i) good and (ii) failing units indicating a signal break on the bad unit along the failure path. (b) FIB Cross-section at the broken signal location along AA'
(a) EBAC analysis comparison between (i) good and (ii) failing units indicating a signal break on the bad unit along the failure path. (b) FIB Cross-section at the broken signal location along AA'

Figure 1263b. (a) EBAC analysis comparison between (i) good and (ii) failing units indicating a signal break on the bad unit along the failure path. (b) FIB Cross-section at the broken signal location along AA'. [2]


 

 

 

 

 

 

 

 

[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.
[2] A. C. T. Quah, G. B. Ang, D. Nagalingam, C. Q. Chen, H. P. Ng, S.P. Neo, J. Lam, Z.H. Mai, Failure Analysis Methodology on Resistive Open Defects, ISTFA 2014: Conference Proceedings from the 40th International Symposium for Testing and Failure Analysis, November 9–13, 2014, Houston, Texas, USA.

 


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