Sample preparation by focused ion beam without argon ion milling for quantitative electron holography of p-n junctions

Abstract

A method is suggested to prepare lamella for quantitative electron holography by focused ion beam without the need for postprocessing. It relies on thinning of a lamella from the back side of the Si substrate and removal of the protective layers with Ga ions with progressively lower energies down to 2 kV. It is shown that variations of the dopant potential across a one-dimensional p+/n junction in Si, which are derived by electron holography and from the results of secondary ion mass spectrometry, agree to much better values than 50 mV. The effect of the protective layer deposited during TEM sample preparation on the results of electron holography was evaluated. The Si oxide protective layer, which was deposited onto the Si surface, showed a limited charging effect while oxidizing the top of the Si surface. The carbon protective layer showed no surface erosion, yet it has revealed strong charging effects. The deposition process of the protective layer needs to be optimized for a given application in future work.