Application of contact-level ion-beam induced passive voltage contrast in failure analysis of static random access memory

The demand for improvement of device speed and reduction of power consumption has driven semiconductor devices to be miniaturized continuously. To develop new process generations, static random access memory (SRAM) is often chosen as the process qualification vehicle because the quality and performance of SRAMs are direct reflections of high density and small feature size, and they are very sensitive to process variation. Therefore, analysis of SRAM failure is a critical time-to market path for process development. During sub-quarter micron process development, the integrity of high aspect ratio contacts was found to be a major concern. For contact defect analysis, focus ion beam (FIB) cross-sectioning is the best method. However, the problem remains of how to identify the defective contact. E-beam testing and optical beam-induced current (OBIC) techniques have been reported as tools for detecting defective contacts. However, few FA labs have such equipment. In this study, a novel technique of contact-level ion-beam induced passive voltage contrast was developed to identify defective contacts employing a FIB station, and its application was demonstrated by SRAM failure analysis.