Imaging high resolution subsurface defects nondestructively in advanced interconnect structures and devices is a challenge and no known metrology tools are available to identify such defects in a nondestructive way at nanometer level. Monitoring these defects necessitate the understanding of their growth mechanism of these interconnects as well as defect formation. We report here the application of scanning near field ultrasound holography by imaging buried defects in copper interconnects and low-K dielectric materials. Defects in these copper lines such as voids and delaminations appear as regions of dark contrast in ultrasound holography imaging due to large acoustic impedance mismatch at the voids. Identification of these buried defects in these interconnect architectures in a nondestructive way will open up unique opportunities in using this technique to detect subsurface defects and material imperfections.

Ultrasound holography for noninvasive imaging of buried defects and interfaces for advanced interconnect architectures

The characteristics of the Si–vacuum interface were compared with the characteristics of the oxide–air interface formed following room temperature oxidation for a variety of samples. Scanning tunneling microscopy was used to measure the surface structure following vacuum preparation, and atomic force microscopy was used to measure the oxide surface on the same samples following exposure to air. Samples investigated included nominally flat Si(111) with equilibrated and quenched surface configurations, Si(111) miscut by 1.25° toward the [211] and equilibrated to yield the faceted structure, and nominally flat Si(001) wafers. In all cases, the step morphology of the clean surfaces was duplicated on the surface of the oxide.

Conformal oxides on Si surfaces

The possibility of modifying existing materials through technology has become the recipe for preparation of advanced materials. Nonequilibrium processing of silicon through MeV ion irradiation will be shown here to yield interesting properties. We propose localiza- tion of vibrational energy following an ion irradiation process and their transport (nonlinear transport of energy) through linear chains of a single-crystalline lattice. The localization of energy can involve 3-4 atoms, and, hence, nanometer-sized entities evolve, distinguishable from the remaining periodic lattice owing to their unique interatomic distances. The energy required to produce these structures is supplied by a single high-energy heavy ion, incident normal to a suitable crystal face so as to lose energy by the electronic energy loss mechanism. These entities can be trapped at a desired location that leads to silicon nanostructures with modified band-gaps.

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Nonequilibrium processes for generating silicon nanostructures in single-crystalline silicon*

We provide experimental evidence for the transport of atomic disorder over large distances, in device grade single-crystalline silicon, following irradiation with 200 MeV silver ions Pile-up of lattice defects or disorder is effected at predetermined locations, spatially separated from the irradiation site These are revealed by STM scans with atomic resolution, of an intermediate region, spanning from irradiated to shadowed parts of the crystal surface The experimental results are consistent with transport of disorder through breather-like intrinsic localised excitations

https://iopscience.iop.org/article/10.1209/epl/i2000-00508-7/pdf

MeV ion-induced movement of lattice disorder in single crystalline silicon

CeO2 nanoparticles coated by sodium bis(2-ethylhexyl) sulfosuccinite have been prepared by using the microemulsion method. An average particle size of 2-3 nm was revealed by using transmission electron microscopy. X-ray diffraction shows that the CeO2 nanoparticles remain the CaF2-type cubic structures as the bulk crystal. Extended X-ray absorption fine structure technique is used to probe the local atomic structures around the absorber Ce. A double Gaussian model is used to deduce the structural parameters of the first coordination shell. Bulk CeO2 with eight oxygen atoms located at 2.338 Angstrom was used as the reference sample to extract the backscattering amplitude and phase shift of the Ce-O bond. Our EXAFS data suggest that in CeO2 nanoparticles, the oxygen coordination number around Ce has no obvious decrease, but the bond-length of Ce-O is obviously elongated. It is postulated that a surface/core model may be used to describe the local atomic structures in the CeO2 nanoparticles. (C) 2000 Elsevier Science S.A. All rights reserved.

EXAFS study on the local atomic structures around Ce in CeO2 nanoparticles

A study of the electronic states near the Fermi level in high- superconductors, which is so important to understanding the mechanism of superconductivity, has been carried out on well characterized single crystals of superconducting . A large number of polarized x-ray absorption spectra have been recorded with the E vector parallel to the a - b plane and perpendicular to it at the Dragon beam line at the Brookhaven Light Source using the fluorescence mode of detection. These bulk spectra of and O K are then analysed to obtain the density of the unoccupied and orbitals from the spectra and the density of the and orbitals from the O K spectra. The results clearly show the presence of orbitals in a substantial amount although the same cannot be said of the orbitals. Tight-binding calculations of the holes are also reported and compared with experimental results.

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Polarized x-ray absorption spectroscopy study of the symmetry of unoccupied electronic states near the Fermi level in the Bi2Sr2CaCu2O8 system

The interface between silicon (100) and thermal silicon dioxide grown by wet, dry, and trichloroethylene oxidation has been investigated by scanning tunneling microscopy and scanning tunneling spectroscopy. The scanning tunneling microscopy images of the silicon surface, after removal of oxide, reveal the presence of silicon bumps (protrusions) in samples prepared by wet and dry oxidation while no protrusions are seen at the interface of trichloroethylene oxidized samples. The spectroscopic measurements predict that these are silicon protrusions and are produced by oxide growth conditions. X‐ray photon spectroscopy on samples containing protrusions also supports the above prediction. Thus, our study suggests that roughness of the silicon–silicon dioxide interface depends on oxide growth conditions and a relatively smooth interface is obtained by tricholoroethylene oxidation.

Scanning tunneling microscopy of Si/SiO2 interface roughness and its dependence on growth conditions

We have synthesized Ca x LaBaCu 3 O ≃7 (x = 0.8 to 1.2) and CaLaBa y Cu 3 O ≃7 (y = 0.8 to 1.2) tetragonal superconducting compounds. Results of XRD, dc resistivity, iodometric titration, and X-ray photoelectron spectroscopy on these compounds have been discussed in detail.

Characterization Studies on the Tetragonal CaLaBaCu3O≈7 Superconductor

Pseudo binary alloys like R(A 1− x B x ) 2 compounds are known to exhibit both negative and positive types of deviation from Vegard's law on substitution of 3d or 4f cations. CeNi 2 based alloys are known to be mixed valence compounds whereas CeFe 2 alloys are probably not. In this study we examine the influence of substitution of rare earth compounds rather than the 3d ions. Ce L III absorption edge XAFS is measured in the single phase Ce 1− x Y x Fe 2 system ( x = 0.0, 0.1, 0.2, 0.3 and 0.7) using the super ACO synchrotron radiation facility at LURE. The spectra are discussed in terms of the change in the Ce valence as a result of progressive substitution by trivalent Y cation. The problem of Ce valence saturation is also addressed in this work.

XAFS study of Ce valence in the Ce1−xYxFe2 system

XANES with polarized synchrotron light is now established to be one of the important techniques for the study of the electronic structure of high-T c superconductors in order to find out the symmetry of holes and their implication to the theoretical models proposed to explain superconductivity in these cuprates. The XANES spectra are measured by two methods in the soft X-ray region, namely, total yield (TY) and fluorescence yield (FY) methods, which give different results with respect to out-of-plane Cu 3d(z 2 ) symmetric holes. The reason of this discrepancy is not quite clear. Polarized XANES measurements on Bi-2212 single crystals at the Cu L 3 edge by the TY and FY methods are reported and the results are discussed in detail.

S. Venkatesh

Papers

Polarized x-ray absorption spectroscopy study of the symmetry of unoccupied electronic states near the Fermi level in the Bi2Sr2CaCu2O8 system

Scanning tunneling microscopy of Si/SiO2 interface roughness and its dependence on growth conditions

Characterization Studies on the Tetragonal CaLaBaCu3O≈7 Superconductor

XAFS study of Ce valence in the Ce1−xYxFe2 system

Polarized XANES Studies of Cu L3 Edges of Bi-2212 Superconducting Single Crystals Using Total and Fluorescence Yield Techniques