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Alignment Accuracy of Focused Ion Beam Implantation

The theoretical alignment limit for focused ion beam (FIB) implantation was deduced from the calculated resolution for the detection of an alignment mark. The alignment resolution varies with the signal to noise ratio and there is an optimum current which gives the best resolution. The alignment resolution εσ is approximately 0.006 µm for a 160 keV Si++ beam from our FIB implanter. The measured alignment error is approximately 0.06 µm and the main reason of this discrepancy is vibration. The ultimate limit on the alignment error can be reached through improvements in the implanter system.