Abstract 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.

Abstract In this work, a slightly unetched gate hard mask failure was analyzed by nano probing. Although unetched hard mask failures are commonly detected from the cross sectional view with FIB or FIB-TEM and planar view with the voltage contrast, in this case of the very slightly unetched hard mask, it was difficult to find the defects within the failed area by physical analysis methods. FIB is useful due to its function of milling and checking from the one region to another region within the suspected area, but the defect, located under contact was very tiny. So, it could not be detected in the tilted-view of the FIB. However, the state of the failure could be understood from the electrical analysis using a nano probe due to its ability to probe contact nodes across the fail area. Among the transistors in the fail area, one transistor’s characteristics showed higher leakage current and lower ON current than expected. After physical analysis, slightly remained hard mask was detected by TEM. Chemical processing was followed to determine the gate electrode (WSi2) connection to tungsten contact. It was also proven that when gate is floated, more leakage current flows compared to the state that the zero voltage is applied to the gate. This was not verified by circuit simulation due to the floating nodes.