Abstract

The Soft Bit failure (Single Bit Failure sensitive to voltage) of a 90nm SRAM cell presented a difficult challenge for the Failure Analysis (FA) group. Physical analysis of these Soft SRAM failures did not show any visual defects; therefore the FA required an accurate electrical characterization. The transistor characteristics of the failing SRAM transistors are needed in order to speculate on the possible failure mechanism. The Nano-Probing technique performed at Nice Device Failure Analysis of Laboratory (NDAL) allowed us to identify anomalies of I/V characteristics like Vt imbalance, low Gain, asymmetrical Vt, ID (Drive current) and Ron. Case studies of an asymmetry phenomenon reported here lead to a correlation between the failure mode and the electrical measurements. This paper demonstrates a suitable electrical methodology and characterization by Nano-Probing in order to successfully manage a FA approach on this type of failure.

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