High resolution RBS investigations of ZrO₂ layer growth in the initial stage on native silicon oxide and titanium nitride

High Resolution Rutherford Backscattering Spectrometry (HR-RBS) with a depth resolution of about 0.3 nm near the surface was used to analyse the interface between ultrathin high-k ZrO₂-layers and the substrate. In order to improve the quality of the analysis, a method was developed that takes local thickness variations, obtained by atomic force microscopy (AFM), into account during simulation of the HR-RBS spectra. The aim was to study atomic layer deposition (ALD) growth processes on Si(100) covered with native silicon oxide (SiO₂) or with TiN. In the first case the interface is sharp, except for a small intermediate ZrSiO₄-layer, and no diffusion of Zr-atoms in SiO₂ could be detected. A quite different behaviour could be derived from high resolution spectra for the growth of ZrO₂ on TiN. In addition, measurements of the surface topography of the TiN-layer revealed non-negligible surface roughness. Diffusion of Zr into polycrystalline TiN was demonstrated for the first time after correction for surface roughness. This observation indicates that already during the first ALD reaction cycle a small proportion of the deposited Zr-atoms diffuses – probably along grain boundaries – into the TiN-layer up to a depth of 3 nm.