DEGRADATION OF VERY THIN GATE DIELECTRICS FOR MOS STRUCTURES DUE TO THROUGH-OXIDE ION-IMPLANTATION

In VLSI technology it is usual to proceed the ion implantation of heav y dopant species through very thin silicon dioxide gate insulators. As a consequence of this process there is a degradation of the insulatin g properties of the oxide which induces an enhanced leakage current in the MOS structures as well as a decrease of the dieleetric breakdown voltage. In the present work we study quantitatively the possible phys ico-chemical causes of these degradation phenomena and of their recove ry by thermal annealing using O-18 isotopic tracing techniques. Films of (SiO2)-O-18 with thicknesses ranging from 4 to 12 nm thermally grow n on (100) Si wafers implanted with As and Sb in the fluences range 10 (14)-10(16) Cm-2. Using nuclear reaction analyses, secondary ions mass spectrometry, nuclear resonance profiling and channeling of cw-partic les with detection at grazing angles we measured the amount of oxygen lost from the silicon dioxide films due to sputtering at the oxide-vac uum interface, the amount of oxygen from the oxide film recoil-implant ed into silicon, the amount of oxygen from the residual gas in the vac uum of the implantation chamber recoil-implanted into the silicon oxid e, and the change in the stoichiometry of the silicon oxide films due to through-oxide implantation. The results of the present work togethe r with the results existing in the literature on the electrical charac terization of the same systems are used to discuss the possible physic o-chemical causes of the observed dielectric loss. The recovery of the stoichiometry of the oxide films by thermal annealing in oxygen atmos pheres after implantation was accomplished and the conditions to do it are also discussed.