Formation of amorphous Yb2O3/crystalline ZrTiO4 gate stack and its application in n-MOSFET with sub-nm EOT

Highlights: • Orthorhombic ZrTiO4 and amorphous Yb2O3 were confirmed by XRD and TEM. • Gate stack of ZrTiO4/Yb2O3 shows low Dit and a small fixed oxide charge density. • MOSFETs with 0.79-nm EOT and excellent sub-Vt swing of 66 mV/dec were realized. • Good reliability is proven by negligible ΔVt, Δgm and sub-Vt swing degradation. - Abstract: Dielectric stack composed of orthorhombic ZrTiO4 and amorphous Yb2O3 interfacial layer was employed as the gate dielectric for Si n-MOSFET. The gate stack with EOT of 0.79 nm demonstrates a desirable dielectric quality in terms of a low interface trap density (Dit) of 2.4 × 1011 cm−2 eV−1 and a small fixed oxide charge density of 2.8 × 1011 cm−2. The promising transistor characteristics are evidenced by the excellent subthreshold swing of 66 mV/dec and good electron mobility of 192 cm2/V s at 1 MV/cm. The former is primarily due to the low Dit value while the latter is ascribed to the small amount of fixed oxide charge and the existence of an Yb2O3 interfacial layer; both factors are beneficial to suppress the carrier remote scattering mechanism. From the analysis of positive bias temperature instability with the stress field of 11 MV/cm for 1000 s at 85 °C, 12-mV shift in threshold voltage and negligible degradation in subthreshold swing and transconductance prove the satisfactory reliability performance. These prominent electrical characteristics show that the crystalline-based gate stack is eligible for aggressively scaled CMOS devices