Characterization of Atomic Layer Deposited Lanthanum Silicate Films for a Gate Oxide of Si and Ge Devices

Abstract

The effect of oxygen sources, i.e. O3 or H2O, on chemical composition, dielectric constant and leakage current density of atomic-layer-deposited La-silicate films on Si substrate was examined. The dielectric constant of La-silicate films grown on Si substrate using O3 was ~ 8.0, which was lower than that of La-silicate films grown using H2O, ~ 11.7 due to the higher Si concentrations. However, leakage current density of La-silicate films grown using O3 was about 3 orders of magnitude lower than that of La-silicate films grown using H2O at an identical capacitance-equivalent-thickness (but almost half the physical thickness), due to the higher Si concentrations and less La-carbonate formation. We have investigated the effects of Si concentrations in La-silicate film formed by ALD on Ge substrate of the electric property especially in reduction of C-V hysteresis. La-silicate film with Si concentration increment (~ 25 % to ~ 35 %) on Ge substrate effectively reduced C-V hysteresis due to suppression of Ge sub-oxide generation calculated from XPS analysis. La-silicate film with very thin Al2O3 interface passivation layer on Ge substrate obtained smaller C-V hysteresis as ~238 mV due to lower interface state density by suppression of Ge sub-oxide formation. BEMAS-SiO2 capping La-silicate film with Al2O3 interface passivation layer showed smaller Ge sub-oxide formation as smaller C-V hysteresis shown. Al2O3 interface passivation La-silicate film and SiO2 capping La-silicate film with Al2O3 interface passivation layer has tendency of low leakage current density. It is also found that the Al2O3 thickness of 1– 2 monolayer and SiO2 capping is critical for the reduction of the interface state density. In conclusion, the ALD-Al2O3 interfacial passivation layer and SiO2 capping, whose thickness can be precisely controlled, is effective for controlling the formation of Ge oxides at high-k/Ge interfaces.