Comparative depth-profiling analysis of nanometer-metal multilayers by ion-probing techniques

Abstract

We examine here the depth resolution (interface width) in elemental analysis and depth profiling of complex layer systems of three ion-probing techniques, each of which has pros and cons: • Rutherford backscattering spectrometry (RBS); • secondary ion mass spectroscopy (SIMS); and, • glow-discharge optical emission spectroscopy (GDOES). RBS is a non-destructive technique that requires no standards for quantification, although access to medium-scale ion-source facilities is needed. SIMS maintains nanometer (nm) resolution at greater depths but at the expense of longer data-acquisition times. Finally, GDOES allows depth profiling quickly and accurately, although depth resolution degrades linearly with depth due to sputtering effects (e.g., crater shape and chemical modifications), among other factors. We discuss these ion-probing techniques in the light of new results obtained with chromium/titanium multilayer structures with individual layer thicknesses between hundreds of nm and a few nm. We resolved ultra-thin chromium layers of 2.5 nm and 5 nm, buried at different depths in titanium matrixes with thicknesses up to 3 μm, and used the results to evaluate the depth resolution of the ion-probing techniques.