FIB failure analysis of memory arrays

Abstract

Many modern microelectronic chips contain embedded memory arrays. A typical memory bit-cell contains several transistors. Failure of a single transistor or contact within a bit cell makes the entire bit cell inoperable. A dual-beam Focused Ion Beam (FIB) tool combines milling capability with in situ Scanning Electron Microscope (SEM) imaging, which is very useful for identifying the root cause when a physical defect is present. This paper describes the slice-and-view FIB technique for failure analysis (FA) in memory arrays. Several failure mechanisms have been identified, including missing patterns, killer particle defects, shorted and open stack vias. Transmission Electron Microscopy (TEM)/Scanning TEM (STEM) analysis was able to provide additional information when SEM resolution was not sufficient. Processes were adjusted appropriately leading to yield enhancement.