J. Hong, S. Cho, Y. Han, H. Choi, S. D. Kwon, H. Kim, T. Kim, S. Son, Samsung Electronics System LSI, Yongin, South Korea

Summary: Using the Nanoprobe technique, transistor characteristic in actual SRAM cell has been directly measured. To define the root causes of marginal soft failure, characterizing transistor level has its limits to understand cell stability and failure mechanism. Moreover, as a shrink of SRAM cell dimension, Electron beam irradiation comes to an important issue. When focused electron beam at SRAM cell for a time, it is affected to change transistor characteristics, such as Vth shift and Idoff, Idsat swing. During probing with SEM based nanoprober, to get correct data, it has to reduce electron beam influence at all possible. As a probing at Metal1 layer, it is possible to avoid electron beam influence, furthermore it allows the coupled analysis of cell stability and TR characteristics. This paper presents the process of measuring SNM (static noise margin), WNM (write noise margin) with 6 pin nanoprober, and characterization & analysis of SRAM cell stability through the case study of 45nm devices SRAM soft failure.