In this article, an analysis of a failure in the embedded SRAM in a CMOS Image Sensor is investigated. The failure was due to unformed CoSi2. Because unformed CoSi2 causes a varying degree of response, a nano-prober was used to find the abnormally operating transistors among a 1-bit SRAM cell consisting of six transistors(6T). After measuring and analyzing the current-voltage relationships between each transistor, the current magnitude of one pull-down transistor was found to be less than the expected range and particularly lower than that of a connected access transistor. To visualize the failure phenomenon and find the root cause of this, TEM analysis was conducted. Using the EELS (Electron Energy Loss Spectroscopy) elemental mapping, unformed CoSi2 was detected between the contact and substrate, where the contact corresponds to the VSS of the pull-down transistor. This caused an increase in the contact resistance, thus lowering the current magnitude of the abnormal transistor to a greater degree than expected.

As semiconductor device geometries shrink due to process technology development and circuit density rapidly increases, it is becoming extremely difficult to effectively analyze defects. Against this background, more precise and efficient techniques to analyze the root cause of defects is in constant demand. This paper proposes a method to quickly and accurately identify the true cause of device failure by using a nano probe EBAC/EBIC analysis technique. The most significant benefit of the EBAC/EBIC analysis technique is the ability to identify normal or abnormal circuit behavior with an intuitive image. This benefit can minimize the damage to a sample during the initial analysis phase, which has been an issue in the analysis of existing physical properties of semiconductors. In this paper, we identified the root cause of a series transistor defect in CIS (CMOS Image Sensor) product by using EBAC/EBIC (analysis) technique, and verified this with the assistance of SSRM (Scanning Spreading Resistance Microscopy) and APT (Atomic Probe Tomography). By doing so, we confirmed that the analysis technique proposed in this paper is very effective in identifying and pinpointing the true cause and location of the defect.