MICROSTRUCTURAL CHARACTERIZATION OF STOICHIOMETRIC BURIED SI3N4 FILMS

The properties of buried stoichiometric Si3N4 layers are studied using Extended X-ray Absorption Fine Structure (EXAFS), Near-Edge X-ray Abs orption Fine Structure (NEXAFS), Infrared Absorption (IR), Nuclear Rea ction Analysis (NRA) and Cross-Section Transmission Electron Microscop y (XTEM). The samples were fabricated with ion-implantation using 200 keV N-15 ions and a fluency of 1.4 x 10(18) at./cm(2) and they were ch aracterized in the as-grown state and after annealing. The N/Si ratio, measured with NRA, is 1.33, which corresponds to stoichiometric nitri des. Analysis of the EXAFS spectra measured at the N-K-edge indicate t hat the samples are stoichiometric to a microscopic scale, i.e. the bo nd lengths and coordination numbers in the Ist and 2nd nearest-neighbo r shells are identical to those of a stoichiometric nitride. After ann ealing at 1200 degrees C for 2 h the alpha-Si3N4 phase is formed, as d etected by IR absorption measurements, while the small concentration o f N-dangling bonds, present in the as-implanted state, are completely annealed out, as indicated by the NEXAFS spectra. However, the EXAFS r esults do not indicate any change in the microstructure of the film. F inally, TEM observations confirm the formation of a nitride layer and reveal the presence of a heavily damaged region in the back interface with the underlying Si layer.