Sub-5-Å La2O3 In Situ Dipole Technique for Large VFB Modulation With EOT Reduction and Improved Interface for HKMG Technology

In this article, an in situ La-dipole technique with atomic-scale atomic layer deposition (ALD) La2O3 in laminated high-
${k}$
dielectric stacks is presented, where the large flat-band voltage (
${V} _{{\text {FB}}}$
) modulation range is observed. Meanwhile, the lower equivalent oxide thickness (EOT) and improvements in other electrical properties are obtained. With the in situ 4.6 Å La2O3 under HfO2, a 710 mV
${V} _{{\text {FB}}}$
negative modulation range and a 0.15-nm EOT reduction are obtained. As for the gate leakage, more than two orders of magnitude decreasing under the same overdrive bias-voltage is achieved, and the same decreasing level of the voltage hysteresis under dual-sweeping is demonstrated for both obviously suppressed trap/detrap electron density (
${N} _{{\text {ot}}}$
) and interface trap density (
${D} _{{\text {it}}}$
) by in situ La-dipole technique. Meanwhile, since the interdiffusion of La atoms and Si atoms was observed by high-resolution transmission electron microscope (HRTEM) image and energy dispersive X-ray (EDX) analysis, an interpretative model with LaSiOx formation by the element interdiffusion between laminated layer is proposed for explaining of electrical characteristics improvement by in situ La-dipole technique. The results exhibit a promising approach for multiple threshold voltage (multi-
${V} _{{\text {t}}}$
) formation and further performance boosting in future nanosheet gate-all-around field effect transistors (NS GAA-FETs).