Dose- and annealing-induced changes in the microstructure of buried SiNx:: An x-ray absorption study

The microstructure and the annealing behavior of N-rich SiNx, films are studied with x-ray absorption measurements at the N-K edge. The SiNx films were fabricated with ion implantation of 35 keV N+ ions into Si substrates, in the dose range 2 x 10(17)-2 x 10(18) ions/cm(2). The near-edge x-ray absorption fine structure (NEXAFS) spectra of the N-rich films are characterized by a strong resonance line (RL2) at 403.3 +/- 0.1 eV whose intensity increases with the implantation dose. RL2 is attributed to dipole electron transitions, from 1s to unoccupied p orbitals, at a defect site containing a N dangling bond defect. The defect related to RL2 has high thermal stability and is practically unaffected by vacuum annealing up to 1000 degrees C. One more defect-related resonance (RL1) is detected at 401.1 +/- 0.3 eV in the films fabricated with the lower and intermediate used implantation doses (2 x 10(17) and 1 x 10(18) cm(-2), respectively). The activation energy for the annealing of RL1 is 0.50 +/- 0.05 eV. Extended x-ray absorption fine structure spectroscopy (EXAFS) on the as-implanted and annealed films reveals that subnitrides are formed upon implantation. These nitrides are characterized by a Si-N nearest-neighbor distance which is comparable to that of the reference nitride, while the coordination number in the first nearest-neighbor shell N-1 depends on the implantation dose. The stoichiometry deviation, as measured from the value of N-1 which takes values between 1.7 and 2.5 for the limiting doses of 2 x 10(18) and 2 x 10(17) cm(-2), respectively, shows the correlation between the RL2 in the NEXAFS spectra and the presence of N dangling bonds in the as-implanted films. (C) 1998 American Institute of Physics. [S0021-8979(98)06611-0].