Effects of plasma-induced damage to ultrathin (≤1.5 nm) gate dielectric on equivalent oxide thickness downscaling using plasma nitridation process

Plasma nitridation was used to increase the dielectric constant of SiO₂ so that the equivalent oxide thickness (EOT) could be reduced. The effects of plasma-induced damage to ultrathin (≤15 A) plasma-nitrided oxide (PNO) on EOT scaling were systematically investigated. The study showed that increasing nitrogen concentrations of PNO using aggressive plasma nitridation failed to reduce the EOT because the plasma-induced parasitic oxidation resulted in a substantial increase in oxide thickness that overrode the dielectric constant increase and consequently increased the EOT. The carrier mobility degradations and higher HF etching rates of PNO demonstrated the damage from plasma nitridation. Although reducing base oxide thickness was able to scale down EOT, the efficiency was extremely poor; a decrease of 1.5 A in base oxide thickness only resulted in 0.3 A of EOT reduction. MOSFET device data and SIMS depth profiles indicated that a thinner base oxide was more susceptible to plasma-induced damage. Finally, this study showed that after optimization, the plasma nitridation process was able to reduce plasma-induced damage so that the EOT could be scaled down without penalties.