Physical and Electrical Properties of Memory Quality PECVD Silicon Oxynitride

Memory quality silicon oxynitride has been deposited using plasma-enhanced chemical vapor deposition (PECVD). The effects of oxygen on the physical properties of the films were studied using ellipsometry, ultraviolet spectrophotome-try, and Fourier transform infrared spectroscopy. Silicon oxynitride films of various compositions were deposited by changing the amount of nitrous oxide in the reactant gas stream from 5 to 85 sccm for a constant value of NH3/SiH4 = 0.8. The refractive index of the films decreases from 1.8 to 1.55 and the deposition rate increases as nitrous oxide flow rate in-creases. The Si--H bond concentration i creases lightly for nitrous oxide flows of 5 to 9 sccm and then decreases for higher flows. The optical bandedge varies monotonically from 3.2 eV for silicon nitride (no N20) to 5.25 eV for a nitrous oxide flow of 85 sccm. Total bonded hydrogen decreases with increasing nitrous oxide flow due to a reduction in Si--H bond concentration. Multiple bonding configurations are observed for silicon and hydrogen at the higher nitrous oxide flows. A correlation is observed between Si--H bond concentration and memory window size. Although the addition of oxygen to silicon nitride enhances endurance performance, high nitrous oxide flows increase the charge decay rate and thus degrade the memory performance. In the early developmental history of metal-nitride-oxide-silicon (MNOS) nonvolatile memory technology, th