High depth resolution analysis of elemental depth distributions in nanocoatings

Elemental depth distributions in thin films and near surface regions can be obtained with Ion Beam Analysis (IBA) techniques using MeV ions. Depth profiling of films of a few nanometres thickness as well as multilayer arrangements in the nanometre scale is possible with high resolution (HR) spectrometers. At the research centre in Dresden-Rossendorf, two systems are available for high depth resolution analysis, one for medium to heavy elements (Z > 13) using elastic scattering of ions at the target atoms and one for light elements (Z < 14) detecting atoms ejected from the sample (recoils). In both cases, an energy resolution of about 1‰ is obtained using magnetic spectrometers which allow sub-nanometre depth resolution and, thus, the characteristics of thin film interfaces. Advantages and limits of HR-depth profiling are presented. As an example, atomic layer deposition (ALD) of the high-k material ZrO₂ has been examined on two different underlayers, i.e. SiO₂ or TiN. From the HR-spectrum it is deduced that fifteen ALD cycles result in 1.5 nm ZrO₂ (3.8 ● 10¹⁵ Zr/cm²) on the SiO₂ surface. In more detail simulation and measured energy distribution of C-ions, scattered on the Zr atoms, are in excellent agreement if ZrO₂ layer thickness fluctuation is taken into account. The latter can be obtained by considering surface roughness obtained from AFM measurements. The mentioned agreement of measured and simulated HR-spectra proves that there is no diffusion of Zr atoms into the SiO₂. In a second example ten ALD cycles of ZrO₂ on TiN were studied. Obviously, the TiN underlay causes two effects as visible in the corresponding HR-spectrum: First, the broad low energy tail of the Zr energy distribution can not be verified by ZrO₂ layer thickness variations. Thus, TiN certainly induces Zr diffusion which takes place probably preferentially along grain boundaries of the titanium nitride. Estimated diffusion depths extend up to 3 nm. Secondly, only ten ALD cycles are enough to deposit 4.1 ● 10¹⁵ Zr/cm² on this backing. This finding supports the interpretation of stimulated Zr grain boundary diffusion into TiN. The last example presents a nanometre multilayer arrangement of Al/Cu/FePt on SiO₂. HR measurements are demonstrated for various elements and their corresponding interfaces in different depths.