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ABSTRACT: An electron spin resonance study has been carried out on heteroepitaxial Si/insulator structures obtained through growth of epi- Lu 2 O 3 films on (111)Si ( ∼4.5 % mismatch) by molecular-beam epitaxy, with special attention to the inherent quality as well as the thermal stability of interfaces, monitored through occurring paramagnetic point defects. This indicates the presence, in the as-grown state, of P b defects (∼5×10<sup>11</sup> cm <sup>-2</sup>) with the unpaired sp<sup>3</sup> Si dangling bond along the [111] interface normal, the archetypical defect (trap) of the standard thermal (111) Si / SiO 2 interface, directly revealing, and identified as the result of, imperfect epitaxy. The occurrence of P b defects, a major system of electrically detrimental interface traps, is ascribed to lattice mismatch with related introduction of misfit dislocations. This interface nature appears to persist for annealing in vacuum up to a temperature T an ∼420 ° C . Yet, in the range T an ∼420–550 ° C , the interface starts to “degrade” to standard Si / SiO 2 properties, as indicated by the gradually increasing P b density and attendant appearance of the EX center, an SiO 2 -associated defect. At T an ∼700 -
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09;° C , [ P b ] has increased to about 1.3 times the value for standard thermal (111) Si / SiO 2 , to remain constant up to T an ∼1000 ° C , indicative of an unaltered interface structure. Annealing at T an >1000 ° C results in disintegration altogether of the Si / SiO 2 -type interface. Passivation anneal in H 2 (405 ° C ) alarmingly fails to deactivate the P b system to the device grade (sub) 10<sup>10</sup> cm <sup>-2</sup> eV <sup>-1</sup> level, which would disfavor c-Lu 2 O 3 as a suitable future high- κ replacement for the a-SiO 2 gate dielectric. Comparison of the thermal stability of the c-Lu 2 O 3 /(111) Si interface with that of molecular-beam deposited amorphous- Lu 2 O 3 /(100) Si shows the former to be superior, yet unlikely to meet technological thermal budget requirements. No Lu 2 O 3 -specific point defects could be observed.
Journal of Applied Physics 06/2010; · 2.17 Impact Factor
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ABSTRACT: Electron spin resonance study on heteroepitaxial Si/insulator structures obtained through the growth of epi- Lu <sub>2</sub> O <sub>3</sub> films on (111)Si ( ∼4.5 % mismatched) by reactive molecular beam epitaxy indicates the presence in the as-grown state of interfacial P<sub>b</sub> defects (∼5×10<sup>11</sup> cm <sup>-2</sup>) with an unpaired sp<sup>3</sup> Si dangling bond (DB) along the [111] sample normal, prototypical of the standard thermal (111) Si / SiO <sub>2</sub> interface. The defects, with density remaining unchanged to anneal in vacuum up to temperatures of T<sub> an </sub>∼420 ° C , directly reveal the nonperfect pseudoepitaxial nature of the interface, laid down in electrically detrimental interface traps. These are suggested to be interfacial Si DBs related to Si misfit dislocations. Alarmingly, defect passivation by standard anneal treatments in H <sub>2</sub> fall short. For higher T<sub> an </sub> , the interface deteriorates to “standard” Si / SiO <sub>2</sub> properties, with an attendant appearance of EX centers indicating SiO <sub>2</sub> growth. Above T<sub> an </sub>∼1000 ° C , the interface disintegrates altogether.
Applied Physics Letters 10/2008; · 3.84 Impact Factor
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ABSTRACT: Ballistic electron emission microscopy (BEEM) and internal photoemission measurements on a 20-nm-thick epitaxial Sc2O3 film on Si (111) show the existence of a lower “tail state” conduction band (CB) extending ∼ 0.9 eV below the upper CB (similar to that reported for amorphous Sc2O3 films), indicating that these states are not simply due to disorder in amorphous films. This lower CB is also found to support elastic hot-electron transport even against an applied electric field, indicating transport via extended rather than localized states.
Applied Physics Letters 07/2007; 91(4):042901-042901-3. · 3.84 Impact Factor
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ABSTRACT: Electron spin resonance of paramagnetic point defects was used to probe (100)Si/LaAlO3 structures with nm-thick amorphous high-dielectric constant (κ) LaAlO3 layers deposited directly on clean (100)Si by molecular beam deposition at ∼100°C. Unlike common high-κ metal oxide/Si entities,
no Pb-type interface defects could be observed in the as-grown state, revealing the absence of an Si/SiO2-type interface in terms of these archetypal Si-dangling bond-type Si/SiO2 interface defects (Pb0, Pb1). This state is found to persist during subsequent thermal treatment (5% O2/N2 mixture) up to T
an∼800°C, indicating a thermally stable abrupt Si/LaAlO3 interface. However, in the range T
an∼800–860°C, a Si/SiO2-type interface starts forming as evidenced by the appearance of Pb0 defects and, with some retardation in terms of T
an, the EX center—an SiO2 associated defect, attesting to significant structural/compositional adaptation. Monitoring the defect density versus T
an indicates the SiO
x
nature of the interlayer to disintegrate again upon heating at T
an≥930°C, possibly related to intensifying crystallization and silicate formation. Despite intensive search, no LaAlO3-specific point defects could be revealed.
Journal of Materials Science Materials in Electronics 06/2007; 18(7):735-741. · 1.08 Impact Factor
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ABSTRACT: Electron tunneling spectroscopy (ETS) was used to study amorphous La Al O <sub>3</sub> and La Sc O <sub>3</sub> thin film gate dielectrics for silicon metal-oxide-semiconductor structure. These gate dielectrics were prepared by molecular-beam deposition on (100) Si substrates. The authors have obtained vibrational modes for amorphous La Al O <sub>3</sub> and La Sc O <sub>3</sub> thin films from the ETS spectra, which provide information about the chemical bonding in these films and the interface with silicon. Traps and defects in amorphous La Al O <sub>3</sub> thin films are revealed in the ETS spectra, and their physical locations and energy levels are identified.
Applied Physics Letters 02/2007; · 3.84 Impact Factor
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Microelectronic Engineering 01/2007; 84:2278. · 1.56 Impact Factor
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G. Lucovsky,
C.C. Fulton,
Y. Zhang,
Y. Zou,
J. Luning, L.F. Edge,
J.L. Whitten,
R.J. Nemanich,
H. Ade,
D.G. Schlom,
V.V. Afanase'v,
A. Stesmans,
S. Zollner,
D. Triyoso,
B.R. Rogers
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ABSTRACT: X-ray absorption spectroscopy (XAS) is used to study band edge electronic structure of high-κ transition metal (TM) and trivalent lanthanide rare earth (RE) oxide gate dielectrics. The lowest conduction band d<sup>*</sup>-states in TiO<sub>2</sub>, ZrO<sub>2</sub> and HfO<sub>2</sub> are correlated with: 1) features in the O K<sub>1</sub> edge, and 2) transitions from occupied Ti 2p, Zr 3p and Hf 4p states to empty Ti 3d-, Zr 4d-, and Hf 5d-states, respectively. The relative energies of d-state features indicate that the respective optical bandgaps, E<sub>opt</sub> (or equivalently, E<sub>g</sub>), and conduction band offset energy with respect to Si, E<sub>B</sub>, scale monotonically with the d-state energies of the TM/RE atoms. The multiplicity of d-state features in the Ti L<sub>2,3</sub> spectrum of TiO<sub>2</sub>, and in the derivative of the O K<sub>1</sub> spectra for ZrO<sub>2</sub> and HfO<sub>2</sub> indicate a removal of d-state degeneracies that results from a static Jahn-Teller effect in these nanocrystalline thin film oxides. Similar removals of d-state degeneracies are demonstrated for complex TM/RE oxides including Zr and Hf titanates, and La, Gd and Dy scandates. Analysis of XAS and band edge spectra indicate an additional band edge state that is assigned Jahn-Teller distortions at internal grain boundaries. These band edges defect states are electronically active in photoconductivity (PC), internal photoemission (IPE), and act as bulk traps in metal oxide semiconductor (MOS) devices, contributing to asymmetries in tunneling and Frenkel-Poole transport that have important consequences for performance and reliability in advanced Si devices.
IEEE Transactions on Device and Materials Reliability 04/2005; · 1.54 Impact Factor
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L. F. Edge,
D. G. Schlom,
R. T. Brewer,
Y. J. Chabal,
J. R. Williams,
S. A. Chambers,
C. Hinkle,
G. Lucovsky,
Y. Yang,
S. Stemmer,
M. Copel,
B. Holländer,
J Schubert
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L. F. Edge,
D. G. Schlom,
S. Rivillon,
Y.L. Chabal,
M. P. Augistin,
S. Stemmer,
T Lee,
M J Kim,
H. S. Craft,
J.-P. Maria,
M. E. Hawley,
B. Holländer,
J Schubert,
K. Eisenbeiser
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ABSTRACT: We have characterized thin films of LaScO 3 and LaAlO 3 which were grown by molecular beam deposition on Si substrates. Samples of LaScO 3 were also grown by pulsed laser deposition on MgO substrates. Using transmission studies between 1.5 and 6 eV, we have established that low temperature deposition leads to a reduced band gap with respect to the bulk crystal. Furthermore, using spectroscopic ellipsometry from 5 to 9 eV we observe substantial differences in near-band gap absorption between thin and thicker films for both materials. We obtain a band gap of 5.84 eV for the thinner film of LaAlO 3 , whereas we find a band gap of 6.33 eV for the thicker film of LaAlO 3 . Similarly we find band gaps of 5.5 and 5.96 eV, respectively, for thin and thick films of LaScO 3 . © 2005 American Vacuum Society.
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ABSTRACT: The thermal stability of high-k gate dielectrics and metal gate stack materials under consideration for ULSI technology must be examined for their integration into the MOSFET process flow. In this study, we evaluate the thermal stability of amorphous lanthanum aluminate (LaAlO 3) thin films and metal gate – Hf based gate dielectric stacks on Si (100). XPS, XRD, AFM, TEM, wet etching and backside SIMS are utilized to evaluate the stack stability upon rigorous rapid thermal anneals (RTA) in flowing N 2 ambient. Al 2 O 3 capped LaAlO 3 thin films show a crystallization dependence on the out-diffusion of La and Al into the underlying Si substrate. Penetration of La and Al are seen above 950 o C RTA for 20 s. Evaluation of uncapped and W capped Ru on Hf-based high-k gate stacks indicate, Ru inter-diffusion below the detection limits of SIMS and substantial W diffusion throughout the gate stack upon a 1000 o C, 10 s RTA in N 2 .
