Thermal stability of rare-earth based ultrathin Lu2 O3 for high- k dielectrics

Lu2O3 thin film was deposited on n -type (100) Si substrates using pulsed laser deposition. A k value of 15.95 with an equivalent oxide thickness (EOT) of 1.10 nm and a current density of 2.6× 10-5 A cm2 at +1 V accumulation bias is achievable for the 4.5 nm thick Lu2 O3 thin film deposited at room temperature after postdeposition annealing at 600 °C in oxygen ambient. Annealing a similar sample at 900 °C caused the EOT and leakage current density to increase to 1.68 nm and 1× 10-4 A cm2, respectively. High resolution transmission electron microscopy analysis has shown that Lu2 O3 film remains amorphous at high temperature annealing at 900 °C. An x-ray reflectivity analysis on a separately prepared sample with lower annealing temperature (800 °C) suggested a formation of Lu-based silicate layer. It is believed that the formation of low- k silicate layer may have contributed to the observed increase in EOT and the reduction in the k value.