Stability of cerium oxide on silicon studied by x-ray photoelectron spectroscopy

Abstract

The silicon-cerium oxide interface is studied using x-ray photoelectron spectroscopy. The oxidation and reduction of species at the interface are examined as a function of annealing temperature both in vacuum and oxygen ambient, in order to determine their relative stabilities. By depositing a very thin CeO 2 film ͑ϳ30 Å͒, the cerium and silicon core level peaks can be monitored simultaneously. The presence of characteristic chemical shifts of the Si 2p peak gives information about any SiO x layer that may form at the interface. The oxidation state of the cerium can be probed from three different areas of the spectrum. From this information we can infer the oxidation state of both the silicon and the cerium. For the first time a complete picture of the interface is obtained. The implications of these findings on the utility of CeO 2 in device applications are discussed.

Silicate-free growth of high-quality ultrathin cerium oxide films on Si(111)

“…However, growth 5,8,9 of high-quality ultrathin films, which is crucial for optimized integration, has so far been considerably impeded by Ce-promoted Si oxidation at the interface, resulting in subsequent silicon oxide and cerium silicate formation. [10][11][12] Yet, despite its higher lattice mismatch of about 2.7% using two silicon lattice constants as reference, 13 cubic Ce 2 O 3 is generally believed to be well suited as a buffer layer for sequential CeO 2 deposition due to its lower oxidation state, potentially avoiding the concomitant evolution of SiO x and CeSi x O y species. These low-k defect phases give rise to significant interfacial charge trapping while lowering the dielectric constant of the film and increasing the effective oxide thickness (EOT) of the metal insulator semiconductor field-effect transistor (MISFET) structure.…”

Role of surface oxygen-to-metal ratio on the wettability of rare-earth oxides

“…This indicates that the ceria sample underwent a partial reduction in state from Ce 4þ to Ce 3þ in UHV, which is consistent with observations of Zhang et al 55 Specifically, it can be seen in Figures 2(a) and 2(b) that the intensity of both the characteristic Ce 3þ peaks v 0 and u 0 increased following overnight relaxation in UHV, while the characteristic Ce 4þ peaks v, v 00 , v 000 , u, u 00 , and u 000 all decreased in intensity. Preisler et al 57 have further correlated the change in the oxidation state from Ce 4þ to Ce 3þ with a net decrease in the O/Ce ratio. Therefore, in view of all these observations, we can say, that the change in cerium chemistry, as seen in Figures 2(a) and 2(b), is consistent with the hypothesis that surface relaxation in UHV caused an overall decrease in the surface O/Ce ratio.…”

Effects of electric field in band alignment measurements using photoelectron spectroscopy

“…The thickness of the ALD oxide is affirmed by using attenuation equations of the substrate peak using the XPS. [17,18] The relaxation energies are determined by assuming them to be half the Auger parameter shifts. [19] The auger parameters are calculated from the oxygen O1s core-level and the OKL 1 L 1 auger peak of the SiO 2 with different thicknesses.…”