Thickness Measurement of Focused Ion Beam Thinned Silicon Crystals Using Convergent Beam.Electron Diffraction and Electron Energy Loss Spectroscopy.

Abstract

<jats:p><jats:bold>1. Introduction</jats:bold></jats:p><jats:p>The FIB (focused ion beam) is now widely accepted as the most site-specific TEM preparation tool and as such proves to be highly valuable when analysing ULSI devices. However, using high-energy Gallium ions for milling induces amorphization of the crystal surfaces. A method able to quantify this surface alteration on silicon using a combination of CBED (convergent beam electron diffraction) and EELS (electron energy loss spectroscopy) is presented. CBED is a powerful tool that also can generate an accurate measure of crystal thickness. EELS can yield the total sample thickness, so from the difference the combined amorphous layers can be assessed. Two sets of application results are presented: the first one is obtained on a FIB thinned sample using an ion energy of 50 keV and the second set of results confirms the validity of the proposed method on a mechanically polished specimen with no subsequent ion milling.</jats:p>