In VLSI technology it is usual to proceed the ion implantation of heavy dopan species through very thin silicon dioxide gate insulators. As a consequence of this process there is a degradation of the insulating properties of the oxide which induces an enhanced leakage current in the MOS structures 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 and of their recovery by thermal annealing using 18O isotopic tracing techniques. Films of Si18O2 with thicknesses ranging from 4 to 12 nm thermally grown on (100) Si wafers implanted with As and Sb in the fluences range 1014 -1016 cm-2. Using nuclear reaction analyses, secondary ions mass spectrometry, nuclear resonance profiling and channeling of α-particles with detection at grazing angles we measured the amount of oxygen lost from the silicon dioxide films due to sputtering at the oxide-vacuum interface, the amount of oxygen from the oxide film recoil-implanted into silicon, the amount of oxygen from the residual gas in the vacuum of the implantation chamber recoil-implanted into the silicon oxide, and the change in the stoichiometry of the silicon oxide 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 used to discuss the possible physico-chemical causes of the observed dielectric loss. The recovery of the stoichiometry of the oxide films by thermal annealing in oxygen atmospheres after implantation was accomplished and the conditions to do it are also discussed.
ASJC Scopus subject areas
- Nuclear and High Energy Physics