Study of the growth of thin nitride films under low-energy nitrogen-ion bombardment

Bombardment of silicon surfaces by low-energy (300–1000 eV) nitrogen ions has been investigated as a potential process for growing ultrathin films at relatively low temperatures (<500°C). The thicknesses and chemical states of the obtained films are analysed using ellipsometry, X-ray Photoelectron Spectroscopy (XPS), and Auger Electron Spectroscopy (AES). All the analyses show that ultrathin (∽ 60 Å) silicon nitride films have been directly grown on silicon substrates. Detailed studies of the influence of different process parameters on the obtained films have been carried out. The thicknesses of the obtained films appear to increase with ion energy. The nitridation is found to be a rapid process which can be divided into two steps. The thicknesses are also observed to vary slightly with substrate temperature. The average active energy of nitridation rates is about 3.5 meV which indicates nonthermal process kinetics. For AES analysis, the films are found to be nitrogen-rich ones with the stoichiometric factor x≈1.7 larger than that of pure silicon nitride (x=1.33). In both AES and XPS studies, the chemical state of the silicon atoms resembles the existence of silicon oxynitride films of low oxygen concentration. The growth mechanism is also discussed briefly.