Abstract
This work presents a detailed study on the chemical composition and bond structures of CeO2/La2O3 stacked gate dielectrics based on x-ray photoelectron spectroscopy (XPS) measurements at different depths. The chemical bonding structures in the interfacial layers were revealed by Gaussian decompositions of Ce 3d, La 3d, Si 2s, and O 1s photoemission spectra at different depths. We found that La atoms can diffuse into the CeO2 layer and a cerium-lanthanum complex oxide was formed in between the CeO2 and La2O3 films. Ce3+ and Ce4+ states always coexist in the as-deposited CeO2 film. Quantitative analyses were also conducted. The amount of CeO2 phase decreases by about 8% as approaching the CeO2/La2O3 interface. In addition, as compared with the single layer La2O3 sample, the CeO2/La2O3 stack exhibits a larger extent of silicon oxidation at the La2O3/Si interface. For the CeO2/La2O3 gate stack, the out-diffused lanthanum atoms can promote the reduction of CeO2 which produce more atomic oxygen. This result confirms the significant improvement of electrical properties of CeO2/La2O3 gated devices as the excess oxygen would help to reduce the oxygen vacancies in the film and would suppress the formation of interfacial La-silicide also.
Highlights
Rare-earth (RE) lanthanum oxide (La2O3) has attracted extensive attention as a promising candidate of gate dielectrics for generation deca-nanoscale complementary metal-oxide-semiconductor (CMOS) applications
This work presents a detailed study on the chemical composition and bond structures of CeO2/La2O3 stacked gate dielectrics based on x-ray photoelectron spectroscopy (XPS) measurements at different depths
We found that La atoms can diffuse into the CeO2 layer and a cerium-lanthanum complex oxide was formed in between the CeO2 and La2O3 films
Summary
Rare-earth (RE) lanthanum oxide (La2O3) has attracted extensive attention as a promising candidate of gate dielectrics for generation deca-nanoscale complementary metal-oxide-semiconductor (CMOS) applications. Oxygen vacancies can induce the out-diffusion of substrate Si into the La2O3/Si interface and the bulk oxide as well These effects will impede the realization of the smallest equivalent oxide thickness (EOT) due to the formation of low-k silicate layer.[5,6,7] Several methods, such as element doping, thermal annealing, and the adoption of alloy forms of complex oxides, have been proposed to resolve these issues.[8,9,10]. To further improve the performance and reliability of devices, it is critical to have a better understanding on the chemical reactions taken place at the interfaces With this connection, this work conducts a detailed study on the bonding structure as well as the chemical composition at different depths of the as-deposited CeO2/La2O3 stack by using x-ray photoelectron spectroscopy (XPS) measurements. By using Gaussian deconvolution technique, we made some further analyses on the distribution of Ce3+ states and Ce4+ states in CeOx layer so as to investigate the material interactions occurred at the CeO2/La2O3 and La2O3/Si interfaces
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