Ion channeling effects on the focused ion beam milling of Cu

Abstract

The use of focused ion beam (FIB) instruments for device modification and specimen preparation has become a mainstay in the microelectronics industry and in thin film characterization. The role of the FIB as a tool to rapidly prepare high quality transmission electron microscopy specimens is particularly significant. Special attention has been given to FIB milling of Cu and Si in the microelectronics arena. Although FIB applications involving Si have been extremely successful, it has been noted that Cu tends to present significant challenges to FIB milling because of effects such as the development of milling induced topographical features. We show evidence that links the occurrence of milling induced topography to the severity of redeposition. Specifically, Cu, which sputters ∼2.5 times faster than Si, exhibits an increased susceptibility to redeposition related artifacts. In addition, the effects and the mechanism of Ga+ channeling in Cu is used to illustrate that Ga+ channeling reduces the sputtering yield, improves the quality of FIB mill cuts, and improves the surface characteristics of FIB milled Cu. Finally, a technique for improving FIB milling across grain boundaries or interfaces using ion channeling contrast is suggested.