Full field chemical imaging of buried native sub-oxide layers on doped silicon patterns

a r t i c l e i n f o Keywords: Semiconductor–insulator interfaces Semiconductor–semiconductor thin film structures Silicon oxides Photoelectron emission Synchrotron radiation photoelectron spectroscopy Photoelectron emission microscopy (XPEEM) Fully energy-filtered X-ray photoelectron emission microscopy is used to analyze the spatial distribution of the silicon sub-oxide structure at the SiO 2 /Si interface as a function of underlying doping pattern. Using a spectroscopic pixel-by-pixel curve fitting analysis, we obtain the sub-oxide binding energy and intensity distributions over the full field of view. Binding energy maps for each oxidation state are obtained with a spatial resolution of 120 nm. Within the framework of a five-layer model, the experimental data are used to obtain quantitative maps of the sub-oxide layer thickness and also their spatial distribution over the p–n junctions. Variations in the sub-oxide thicknesses are found to be linked to the level and type of doping. The procedure, which takes into account instrumental artefacts, enables the quantitative analysis of the full 3D dataset. In silicon based micro-and nanotechnologies, the control of the quality and thickness of the SiO 2 /Si interface is of prime importance. An interface of several atomic layers, with a high defect concentration can result in fixed charges and contribute significantly to variations in electrical properties. One of the limits on CMOS downscaling is the quality of the interface. The chemistry of the SiO 2 /Si interface has already been studied in the laboratory using both angle-resolved X-ray photoelectron spectroscopy (XPS) with Al Kα or Mg Kα X-ray sources and synchrotron radiation-based photoelectron spectroscopy (PES). The use of XPS to obtain accurate values for the thickness of the SiO 2 layer and the sub-oxide interfaces has attained extremely high standards in order to define a universal method independent of specific laboratory conditions [1]. The precision now possible in measuring oxide layer thickness is smaller than typical variations in silicon oxygen bond lengths. Photoelectron spectroscopy is also non-destructive, allowing complementary analyses such as Secondary ion mass spectrometry (SIMS) to be performed a posteriori. Synchrotron radiation is particularly useful for a detailed analysis of the SiO 2 /Si interface since the depth probed can be changed by tuning the photon energy. Valence band PES gives information on the density of states and the valence band offsets, in particular on the presence of interface dipoles [2,3]. Finally, the width of the photoelectron spectrum may be measured and thus the work …