Focused Ion Beam Induced Copper Artifact Dose Study

Extract

Reduced feature dimensions in microelectronic devices has led to a growing reliance on the focused ion beam (FIB) for scanning electron microscopy (SEM) and transmission electron microscopy (TEM) specimen preparation. The introduction of copper for use in electrical interconnects will increase this reliance. Copper, much more so than aluminum, tends to smear when conventional polishing techniques are employed, rendering mechanical polishing unsuitable for quality specimen preparation.

The sputtering characteristics of copper differ greatly from the aluminum based materials currently in use. Copper exhibits a grain orientation dependent sputtering rate that tends to produce uneven FIB polished surfaces. The sputtering rate for copper is also much higher than the silicon and dielectric materials that must be simultaneously removed. These differences in sputtering rates lead to the formation of curtains and ledges that also affect specimen quality.

Another FIB induced artifact was observed when preparing SEM specimens (Figure 3).