High-Temperature Processing Effects on Lanthanum Silicate Gate Dielectric MIS Devices

Abstract

The high-temperature stability of MIS devices based on lanthanum silicate having sub-nm (0.6 - 0.7 nm) EOT values are reported. After a 1000{degree sign}C, 10 s RTA treatment, devices with Ta gate metal undergo an EOT increase to 1.57 nm or higher, while devices having TaN as the gate electrode retain an EOT as low as 1.12 nm. An EOT under 1.0 nm is achieved if the 1000{degree sign}C RTA is reduced to 5 s, with a corresponding gate leakage of 0.1 A/cm2. Medium energy ion scattering and X-ray diffraction analysis reveal that the Ta gate metal undergoes a phase change and reaction above 800{degree sign}C, while for TaN no change in the XRD spectrum is detected. Interface state defect densities and leakage currents are reduced after the high temperature processing. Results reveal the importance of the entire gate stack design and processing in obtaining good device properties.