The Effects of Ion Implantation Through Very Thin Silicon Oxide Films

The ion implantation of heavy dopant species through very thin silicon oxide gate insulators d?grades the insulating properties of the oxide inducing an enhanced leakage current in MOS siructures as well as a decrease of the dielectric breakdown voltage. In the present work we study quantitatively the possible physico-chemical causes of these degradation phenomena a l d of their recovery by thermal annealing using isotopic tracing techniques. Films of with thicknesses ranging from 4 to 10 nm thermally grown on (100) silicon wafers were irnplanted with As and Sb to fluences between 1014 and 1016 Using nuclear reaction aialyses, secondary ions mass spectrometry, nuclear resonance profiling and channeling of a-particles with detection a t grazing angles we measured the amount of oxygen lost from the silicon dioxide films due to sputtering a t the oxide-vacuum interface, the amounts of oxygen r6 coil-implanted into silicon from the oxide film and into the silicon oxide from the residual gits in the implantation chamber, and the change in the stoichiometry of the silicon dioxide films due to through-oxide implantation. The results of the present work together with the results existing in the literature on the electrical characterization of the same systems are u!;ed to discuss the possible physicochemical causes of the observed dielectric loss, and sclme preliminary results on the recovery of the dielectric characteristics of the oxide films b:r thermal annealing in oxygen atmospheres after implantation are also discussed.