Thermal stability of rare-earth based ultrathin Lu2O3 for high-k dielectrics

Abstract

Lu 2 O 3 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 1.10nm and a current density of 2.6×10−5A∕cm2 at +1V accumulation bias is achievable for the 4.5nm thick Lu2O3 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 1.68nm and 1×10−4A∕cm2, respectively. High resolution transmission electron microscopy analysis has shown that Lu2O3 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.