Structure of Al2O3 thin layers synthesized on the silicon surface by atomic layer deposition

The distribution of the phase and chemical composition at an Al2O3/Si interface is studied by depth-resolved ultrasoft x-ray emission spectroscopy. The interface is formed by atomic layer deposition of Al2O3 films of various thicknesses (from several to several nanometers to several hundreds of nanometers) on the Si(100) surface (c-Si) or on a 50-nm-thick SiO2 buffer layer on Si. L2,3 bands of Al and Si are used for analysis. It is found that the properties of coatings and Al2O3/Si interfaces substantially depend on the thickness of the Al2O3 layer, which is explained by the complicated character of the process kinetics. At a small thickness of coatings (up to 10–30 nm), the Al2O3 layer contains inclusions of oxidized Si atoms, whose concentration increases as the interface is approached. As the thickness increases, a layer containing inclusions of metallic Al clusters forms. A thin interlayer of Si atoms occurring in an unconventional chemical state is found. When the SiO2 buffer layer is used (Al2O3/SiO2/Si), the structure of the interface and the coating becomes more perfect. The Al2O3 layer does not contain inclusions of metallic aluminum, does not vary with the sample thickness, and has a distinguished boundary with silicon.