Investigations of Work Function Shift in Lanthanum Silicate High-K Dielectric MIS Capacitors

Abstract

The effective work function for lanthanum silicate high-k dielectric MIS capacitors with TaN electrodes is reported in comparison to devices with thin lanthanum oxide capping layers on HfSiO and HfSiON dielectric layers. For the hafnium-based dielectrics, La2O3 capping results in a Vfb shift of up to -184 mV after a 1000 {degree sign}C, 5 sec anneal in nitrogen. LaSiOx films were formed by reacting La2O3 and a chemical oxide. Annealing of these films resulted in a negative Vfb shift of higher magnitude. Ozone or ammonia pretreatment of the chemical oxide prior to silicate formation reduces the magnitude of the shift, allowing for effective work function values between 3.75 and 4.25 eV after annealing. After a 700 {degree sign} C, 10 sec anneal, work function tuning of +/- 150 mV was a achieved while maintaining EOT (0.9 nm) and leakage (0.6 A/cm2 at Vfb + 1 V) for all samples with and without pretreatments.