Ion channeling effects on the focused ion beam milling of Cu

Abstract

Articles you may be interested inMilling of submicron channels on gold layer using double charged arsenic ion beam The use of focused ion beam ͑FIB͒ 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 ϳ2.5 times faster than Si, exhibits an increased susceptibility to redeposition related artifacts. In addition, the effects and the mechanism of Ga ϩ channeling in Cu is used to illustrate that Ga ϩ 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.

Focused Ion Beam Microscopy and Micromachining

“…21 The sputtering yield at a given incidence angle can vary by as much as a factor of 10 for strongly channeling crystal orientations in materials such as Cu. 23 This is because for easy channeling orienta- tions, the ion experiences only inelastic glancing-angle collisions with the atoms lying in a crystal plane and travels deeper into the crystal before causing elastic collisions, so that fewer atoms are sputtered from the surface. This is analogous to the effect of crystal orientation on low-energy electron yields illustrated in Figures 4a and 4b.…”

The Correlation between Ion Beam/Material Interactions and Practical FIB Specimen Preparation

“…Conversely, compounds that are characterized by wide phase fields, nondirectional bonding~i.e., ductile metals!, and few atoms per unit cell can withstand a greater degree of chemical and structural perturbation. Such materials will generally accumulate radiation induced lattice defects but remain crystalline during ion bombardment~Brimhall et al, 1983;Nastasi et al, 1996a;Kempshall et al, 2001!.…”

Focused Ion Beam Nanofabrication Technology

“…However, the ISE imaging shows stronger channeling contrast from crystals than the SE imaging. Because crystal contrast changes with the ion beam incidence angle, where the FIB penetration depth's variation would influence the secondary electron emission rate, the contrast due to crystal orientation in ISE image can be easily distinguished while SE image cannot (Volkert and Minor 2007;Kempshall et al 2001). FIB imaging can offer complementary information about a sample surface, which can be effectively applied in the IC chips' analysis, alloy material science, etc.…”