XPS investigation with factor analysis for the study of Ge clustering in SiO2

Oswald, Steffen; Schmidt, Bernd; Heinig, Karl-Heinz

doi:10.1002/(sici)1096-9918(200004)29:4<249::aid-sia735>3.0.co;2-5

Cited by 30 publications

(2 citation statements)

References 17 publications

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“…The band initiates sharply with large nanocrystals and the sizes smoothly decrease with depth. Similar observations were previously reported by Heinig et al [10,11], who convincingly concluded that the oxidation of dissolved Ge via in-diffusion of oxygen suppresses nanocrystal formation near the surface.…”

Section: Discussionsupporting

confidence: 90%

Liberation of Ion Implanted Ge Nanocrystals from a Silicon Dioxide Matrix via Hydrofluoric Acid Vapor Etching

et al. 2003

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A method to liberate germanium (Ge) nanocrystals from silicon dioxide (SiO2) thin films by hydrofluoric acid (HF) vapor etching is presented. Multi-energy implantation of mass separated Ge ions into 500-nm-thick wet oxide layers on silicon (Si) substrates followed by thermal annealing produces nanocrystals that are 2 to 8 nm in diameter. Raman spectra exhibit the expected asymmetric line shapes due to the phonon confinement effect, but with a higher peak frequency than predicted. To free the nanocrystals, samples are etched in HF vapor to selectively remove the SiO2 matrix and expose the nanocrystal surfaces. Raman spectra of etched samples display peak frequencies consistent with relief of compressive stress. The liberated nanocrystals show long-term stability under ambient atmospheric conditions. Ge nanocrystals can be removed from etched surfaces using an ultrasonic methanol cleaning procedure. The nanocrystal-containing solution is applied to a TEM grid and the solvent is evaporated. Subsequently obtained electron diffraction patterns confirm that the nanocrystals survive this transfer step. Thus, liberated Ge nanocrystals are expected to be accessible for a wide range of manipulation processes and direct characterization techniques.

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Section: Discussionsupporting

confidence: 90%

Liberation of Ion Implanted Ge Nanocrystals from a Silicon Dioxide Matrix via Hydrofluoric Acid Vapor Etching

et al. 2003

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“…(i) Recent Time of Flight Secondary Ion Mass Spectroscopy measurements on low-energy, low-fluence 30 Si + as-implanted SiO 2 samples indicate that only a fraction of about 0.5 − 0.7 of the nominal Si + fluence has been implanted into the SiO 2 [17]. (ii) It is known that (Si or Ge) NC formation in very thin SiO 2 films is extremely sensitive to humidity absorbed by the as-implanted (damaged) glass network [19] as well as to oxidants being present either in the annealing ambient [18].…”

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Multi-dot floating-gates for nonvolatile semiconductor memories: Their ion beam synthesis and morphology

Müller

Bonafos

Heinig

et al. 2004

Applied Physics Letters

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Scalability and performance of current flash memories can be improved substantially by replacing the floating poly-Si gate by a layer of Si dots. This multi-dot layer can be fabricated CMOS-compatibly in very thin gate oxide by ion beam synthesis (IBS). Here, we present both experimental and theoretical studies on IBS of multidot layers consisting of Si nanocrystals (NCs). The NCs are produced by ultra low energy Si + ion implantation, which causes a high Si supersaturation in the shallow implantation region. During post-implantation annealing, this supersaturation leads to phase separation of the excess Si from the SiO 2 . Till now, the study of this phase separation process suffered from the weak Z contrast between Si and SiO 2 in Transmission Electron Microscopy (TEM). Here, this imaging problem is resolved by mapping Si plasmon losses with a Scanning Transmission Electron Microscopy equipped with a parallel Electron Energy Loss Spectroscopy system (PEELS-STEM). Additionally, kinetic lattice Monte Carlo simulations of Si phase separation have been performed and compared with the experimental Si plasmon maps. It has been predicted theoretically that the morphology of the multidot Si floating-gate changes with increasing ion fluence from isolated, spherical NCs to percolated spinodal Si pattern. These patterns agree remarkably with PEELS-STEM images. However, the predicted fluence for spinodal patterns is lower than the experimental one. Because oxidants of the ambient atmosphere penetrate into the as-implanted SiO 2 , a substantial fraction of the implanted Si might be lost due to oxidation.Metal-Oxide-Silicon Field-Effect-Transistors (MOSFETs) with an electrically isolated ("floating") gate layer embedded in the gate oxide are currently used as flash memories. The replacement of this floating-gate by a layer of discrete Si nanocrystals (NCs) [1] improves the performance of flash memories substantially [2]. The reduced probability for a complete discharging of the multi-dot floating-gate by oxide defects allows thinner tunnel oxides. In turn, the floatinggate will be charged/discharged by quantum mechanical direct electron tunneling (instead of defect-generating FowlerNordheim tunneling). The memory operation voltage can be reduced and scalability is improved. Using ion beam synthesis, the multi-dot floating-gate can be fabricated along with standard CMOS processing [3]. Si + ions are implanted at ultra low energies into the gate oxide, causing there a high Si supersaturation. During post-implantation annealing, this Si supersaturation leads to phase separation of elemental Si from SiO 2 [4]. Imaging this phase separation process is difficult. Till now, Transmission Electron Microscopy (TEM) has suffered from weak Z contrast between Si and SiO 2 phases. Recently, this problem was partially overcome by Fresnel imaging using under-focused bright field conditions [5]. Thus, the distance of the layer of phase separated Si from the transistor channel could be determined [6,7]. However, this technique fails to resol...

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X‐Ray Photoelectron Spectroscopy in Analysis of Surfaces

Oswald

2000

Encyclopedia of Analytical Chemistry

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X‐ray photoelectron spectroscopy (XPS) is an analytical technique that uses photoelectrons excited by X‐ray radiation (usually Mg Kα or Al Kα) for the characterization of surfaces to a depth of 2–5 nm. Elemental identification and information on chemical bonding are derived from the measured electron energy and energy shifts, respectively. The use of ultrahigh vacuum (UHV) during analysis requires special sample handling. Depth profiling is possible using ion sputtering. In contrast to the most popular surface analytical technique, Auger electron spectroscopy (AES), nonconducting material can be investigated, little material damage occurs, and the chemical shifts are easier to interpret. However, the lateral resolution of AES (typically 50 nm) is much greater than for XPS (50 µm for standard equipment, down to lower than 3 µm for dedicated instruments). The detection limit (of about 0.1 atom %) is not as low as for mass spectroscopic techniques, but the quantification from XPS peak area measurements is much better, even disclaiming standard sample measurements. This article briefly discusses the principles of the technique, sample requirements, and the typical measuring strategy. Possible information sources (elements, chemical bonding, depth and lateral distributions) are described and their quantification principles are summarized. The main part deals with typical applications relating to several material classes (metals, semiconductors, insulators, polymers) to give a feeling for the effectiveness of the method over a wide range of research and technological problems. A comparison with similar techniques is given as a summary. Technological developments in electronics, nanotechnology, polymers, biotechnology and medicine are all concerned with surface‐related phenomena, suggesting sustained interest in XPS in the foreseeable future.

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XPS investigation with factor analysis for the study of Ge clustering in SiO2

Cited by 30 publications

References 17 publications

Liberation of Ion Implanted Ge Nanocrystals from a Silicon Dioxide Matrix via Hydrofluoric Acid Vapor Etching

Liberation of Ion Implanted Ge Nanocrystals from a Silicon Dioxide Matrix via Hydrofluoric Acid Vapor Etching

Multi-dot floating-gates for nonvolatile semiconductor memories: Their ion beam synthesis and morphology

X‐Ray Photoelectron Spectroscopy in Analysis of Surfaces

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