EFFECTS OF ION-IMPLANTATION ON DEEP-SUBMICROMETER, DRAIN-ENGINEERED MOSFET TECHNOLOGIES

The effects of ion implantation of the reliability of thin-oxide (7-nm) MOS structures employing drain engineering (e.g., LDD, Inverse-T, LATID) have been examined. High-dose, conventional source/drain implants with no spacer present were seen to severely degrade oxide integrity by increasing the gate-to-diffusion leakage along the gate perimeter. The oxide degradation results in a reduction of the oxide breakdown strength rather than an increase in the parameter shorting defect density. The magnitude of the reduction of E(bd) was greatest for the heaviest, highest dose and energy implants. For a 10(15) As/cm2 implant, the dielectric strength of 7-nm oxide dropped from 15 to 9 MV/cm. Gate oxide integrity is improved if oxide spacer technologies are employed prior to source/drain implantation. To be fully effective these spacers must be thick enough to stop ion penetration at the edge of the polysilicon gate. Oxide spacers grown by reoxidation produce structures that are significantly more resistant to ion-implant-induced gate-oxide degradation than oxide spacers formed by CVD oxide. The bird's beak which forms during the reoxidation step is thought to improve gate reliability by thickening the gate oxide at the gate-feature edge. No yield loss could be observed for the low doses (< 10(14) As/cm2) used for LDD implants. Inverse-T and GOLD type structures employ geometries such that the very edge of the gate oxide is not protected by a spacer and is exposed to direct ion impact. These devices exhibit the same edge degradation as conventional devices but are further impacted by the implant which penetrates the thin T-bar.