Low-energy N2 Research Articles

Deposition of silicon oxynitride films by low energy ion beam assisted nitridation at room temperature

The possibility is studied of growing thin silicon oxynitride films by e-gun evaporation of SiO and SiO2 together with concurrent bombardment with low energy N2+ ions from a cyclotron resonance (ECR) source at room temperature of substrates. The degree of nitridation and oxidation of the films is investigated by means of X-ray spectroscopy. The optical characteristics of the films, their environmental stability and adhesion to different substrates are examined. The results obtained show than the films deposited are transparent. It is found that in the case of SiO evaporation with concurrent N2+ ion bombardment, reactive implantation of nitrogen within the films takes place at room temperature of the substrate with the formation of a new silicon oxynitride compound even at low ion energy (150-200 eV).

Circular dichroism of diglycosyl dichalcogenides in solution and solid state

Solution and solid-state CD spectra of nine peracetylated and deacetalyted diglycosyl disulfides were measured to study the relationship between the low-energy CD transitions (n1-->sigma*(S--S) and n2-->sigma*(S--S)) and helicity of the inherently chiral disulfide chromophore as perturbed by chiral carbohydrate moieties. The solid-state CD spectra were directly correlated with the reported X-ray structures of Ac4GlcSSGlcAc4 and Ac4GlcSSGalAc4, and the CD data revealed that all the disulfides have M helicity with C1--S--S--C1' dihedral angles -90 degrees < phi < 0 degrees both in solution and in the solid state. A TDDFT CD study was carried out on dimethyl diselenide which confirmed that the same quadrant rule is relevant between the signs of the low-energy CD transitions and the diselenide torsional angle as formulated previously for the disulfide chromophore. The CD spectra of Ac4GlcSeSeGlcAc4 measured in solution and in the solid state were correlated with its X-ray structure and reproduced well by TDDFT CD calculations performed on its tetra-O-acetyl derivative.

Low energy N2 ion bombardment for removal of (HfO2)x(SiON)1−x in dilute HF

The ion assisted wet removal of (HfO2)x(SiON)1−x high dielectric constant (k) materials and its effect on electrical properties were investigated. Crystallization temperature of (HfO2)x(SiON)1−x increased as the percentage of SiON increased. The crystallized (HfO2)0.6(SiON)0.4 was damaged and turned to an amorphous film via incorporation of N species into the film by N2 plasma treatment. In addition, the structure of (HfO2)0.6(SiON)0.4 was disintegrated into HfO2, SiO(N), and ON after N2 plasma treatment. N2 plasmas using low bias power were applied for wet removal of high-k films and the mechanism of the ion assisted wet removal process was explored. When high bias power was applied, the surface of source and drain regions was nitrided via the reaction between N and Si substrates. Feasibility of the low bias power assisted wet removal process was demonstrated for short channel high-k metal oxide semiconductor device fabrication by the smaller shift of threshold voltage, compared to the high bias power as...

Low-damage atomic layer modification of self-assembled monolayer using neutral beam process

Damage-free surface nitridation of terphenyl methanethiol self-assembled monolayers (TP1-SAMs) was investigated using a novel low-energy N2 neutral beam (NB) irradiation technique. When a conventional inductively coupled plasma process was used, x-ray photoelectron spectra confirmed that the TP1-SAM was quickly broken because ions or ultraviolet (UV) photons enhance the surface decomposition and molecular desorption. Conversely, with the N2 NB radiation process, which is free of ions and UV photons, there was little difference in the atomic ratios of x-ray photoelectron spectra before and after NB irradiation. These results suggest that low-damage surface modification is possible through the authors’ NB technique.

WhyN2Molecules with Thermal Energy Abundantly Dissociate on W(100) and Not on W(110)

Low-energy N2 molecules easily dissociate on W(100) but not on W(110). In this Letter, the six-dimensional potential energy surface for the dissociation of N2 molecules on W(110) has been determined by density functional calculations. Results are compared to those of N2 dissociation on W(100). The difference in reactivity between the two faces is shown to arise from the characteristics of the potential energy surface far from the surface (>3 A) and not from the properties of a precursor well or those of the final atomic adsorption sites.

Secondary electron emission and photoemission studies on surface films of carbon nitride

The secondary electron emission yield of fullerene, graphite, and diamondlike carbon after low-energy N2+ ion bombardment was studied for antimultipactor applications. Nitrogen incorporation into the carbon thin films decreases their secondary emission yield, contrary to the hydrogen or oxygen effect. Carbon nitride surface textured to a nanometric scale had the property of hindering secondary electron emission. Valence bands obtained from photoemission spectroscopy using synchrotron radiation were correlated with secondary electron emission measurements. Multipactor threshold power for carbon nitride was 7.5kW.

Carbon 1s X-ray Photoemission Line Shape Analysis of Highly Oriented Pyrolytic Graphite: The Influence of Structural Damage on Peak Asymmetry

C 1s XPS spectra of various highly oriented pyrolytic graphite (HOPG) surfaces, untreated, as well as those treated by keV Ar+ beam bombardment and low-energy O2, N2, Ar, and H2O plasmas, have been systematically studied by comparing two XPS peak-fitting procedures. These procedures treat the spectrum as either (1) the overlap of several symmetric component peaks or (2) a single asymmetric peak. The results indicate that, in the case of HOPG, the asymmetry parameter defining the single peak is directly related to the extent of damage to the alternant hydrocarbon structure of the HOPG surface, as manifested by its correlation with the symmetric peak component due to the damaged HOPG structure.

Formation of Aluminum Nitride Film for High Power Soft X-Ray Source Using Ion-Beam Assisted Deposition Method

An aluminum nitride (AlN) target for Al-Kα X-ray source with high power and long service life has been developed by N2 + ions assisted Al vapor deposition method (IBAD). The AlN film formations were carried out at the Al deposition rate varied from 2.0 nm/s to 0.15 nm/s with a fixed low-energy N2 + ion of 1 keV. The films were deposited on Cu substrate at room temperature. The AlN films were characterized by an X-ray diffraction, an electron probe X-ray microanalysis and a Knoop-hardness measurement. The AlN deposited at the Al deposition rate of 0.5 nm has a N/Al ratio of 0.4, a Knoop-hardness of ~1500 and a low resistance of ~0.2 . Comparison of durability test between the AlN target and a conventional Al target was performed. It has been revealed, after 500 hours under an electron bombardment of 300 mA at 20 kV, that there were no change of morphology and X-ray intensity on the AlN-surface whilst cracks due to the heat-cycle fatigue covered the Al-surface.

Oxidation-enhanced diffusion of boron in very low-energy N2+-implanted silicon

In this article we study the interstitial injection during oxidation of very low-energy nitrogen-implanted silicon. Buried boron δ layers are used to monitor the interstitial supersaturation during the oxidation of nitrogen-implanted silicon. No difference in boron diffusivity enhancement was observed compared to dry oxidation of nonimplanted samples. This result is different from our experience from N2O oxynitridation study, during which a boron diffusivity enhancement of the order of 20% was observed, revealing the influence of interfacial nitrogen on interstitial kinetics. A possible explanation may be that implanted nitrogen acts as an excess interstitial sink in order to diffuse towards the surface via a non-Fickian mechanism. This work completes a wide study of oxidation of very low-energy nitrogen-implanted silicon related phenomena we performed within the last two years [D. Skarlatos, C. Tsamis, and D. Tsoukalas, J. Appl. Phys. 93, 1832 (2003); D. Skarlatos, E. Kapetanakis, P. Normand, C. Tsamis, M. Perego, S. Ferrari, M. Fanciulli, and D. Tsoukalas, J. Appl. Phys. 96, 300 (2004)].

Low-energy nitrogen ion implantation of InSb

The modification of the electronic properties of InSb by implantation of low-energy N2+ ions and annealing have been investigated. A non-uniform electron density depth profile is observed in the near-surface region. Detailed measurements of the conduction-band electron-plasma frequency as a function of temperature combined with carrier statistics reveal that the electron concentration profile in the near-surface region cannot be explained solely by donor-type defects induced by the nitrogen implantation. However, these experimental observations can readily be explained in terms of InNxSb1−x band structure, the different distributions of damage-induced donor defects, and the acceptor-type nitrogen.

Low-energy ion beam treatment of α-Al2O3(0001) and improvement of photoluminescence of ZnO thin films

A low energy N2 − ion beam impinged on a α-Al2O3(0001) single crystal surface in the range of fluence 5×1015/cm2−1×1018/cm2 at room temperature. After ion bombardment, chemical bonding on the modified sapphire surface was investigated by x-ray photoelectron spectroscopy. Below a fluence of 1×1015/cm2, only a non-bonded N1s peak at the binding energy 398.7 eV was found, but further irradiation up to 2×1017/cm2 induced Al−O−N bonding at around 403 eV. The occurrence of Al−N bonding was identified at ion fluence higher than 5×1017/cm2 at 396.6 eV. II–VI ZnO thin films were grown on an untreated/ion-beam-induced sapphire surface by pulsed laser deposition (PLD) for the investigation of the modified-substrate effect on photoluminescence. The ZnO films grown on modified sapphire containing Al−O−N bonding only, and both Al−O−N and Al−N bonding showed a significant reduction of the peak related to deep-level defects in photoluminescence. These results are explained in terms of the formation of Al−N−O and Al−O−N layers and relaxation of the interfacial strain between Al2O3 and ZnO.

Oxidation of nitrogen-implanted silicon: Comparison of nitrogen distribution and electrical properties of oxides formed by very low and medium energy N2+ implantation

In a previous work [Skarlatos et al., J. Appl. Phys. 93, 1832 (2003)] we investigated the influence of implantation energy on oxide growth and defect formation in nitrogen-implanted silicon substrates. It was shown that as the implantation energy decreases from medium to very low values the oxide reduction decreases. This was attributed to nitrogen out-diffusion, which is more effective when nitrogen is placed closer to the silicon surface. On the other hand very low implantation energy avoids the formation of dislocation loops in the silicon substrate, a key point for modern devices performance. In this second part we compare the nitrogen distribution and electrical properties of ultrathin (25–30 Å) oxides grown under the same oxidation conditions on very low (3 keV) and medium (25 keV) energy nitrogen-implantated silicon. Nitrogen distribution measurements show that a lower content of nitrogen remains within the oxides formed using 3 keV energy as compared to the 25 keV case supporting the results of the first part of this work. So at very low implantation energy the same oxide thickness is obtained increasing the implantation dose. On the other hand oxides formed through very low energy implants show superior electrical properties in terms of surface states and leakage currents due to the lower damage induced in the silicon substrate.

強力軟Ｘ線源の開発―ＡｌＮ／Ｃｕターゲット

An AlN target for Al-Kα x-ray source with high power and long service life has been developed by means of N2+ ions assisted Al vapor deposition method. Ambient temperature formations of AlN on a Cu cold-anode were carried out at Al deposition rate varied from 2.0 nm/s to 0.15 nm/s with fixed low-energy N2+ ion of 1 keV. The AlN films were characterized by an x-ray diffraction, an x-ray fluorescence and a Knoop-hardness measurement. The AlN deposited at Al deposition rate of 0.5 nm has N/Al ratio of 0.45, Knoop-hardness of 1500 and low electric resistance of 0.2 Ω. Comparison of durability test with the AlN target and a conventional Al target was performed by bombarding the targets with 40 keV electrons. It was found that a maximum electron input power of the test increased five times higher than that of Al/Cu target in conventional using model.

Effect of low-energy N2+ ion beam bombardment on silicate glass thin films studied by x-ray photoelectron spectroscopy

Thin film borophosphosilicate glasses, SiOxByPz, have been obtained by chemical vapor deposition on (100) Si substrates. The interaction of low-energy N2+ ions with these films has been studied by x-ray photoelectron spectroscopy (XPS) and infrared spectroscopy. Determination of the chemical composition of the borophosphosilicate glasses was done by qualitative and quantitative XPS analysis. The differences in composition between the films before and after the bombardment have been explained in terms of the relative thermodynamic stability of the compounds present in the sample.

Electron Field Emission of CNx Thin Films Prepared by Low PressurePlasma Enhanced Chemical Vapour Deposition

CNx thin films were prepared using low pressure plasma enhancedchemical vapour deposition, and then bombardedby low-energy N2+. The compositions before and after N2+bombardment were compared using x-ray photoelectron spectroscopy. Theelectron field emission characteristics of CNx thin films before andafter N2+ bombardment were studied under the pressure of 10-6 Pa.For the samples, the turn-on emission field decreased from 2.5 V/µmto 1.2 V/µm while the stable current density increased from0.5 mA/cm2 to a value larger than 1 mA/cm2 before and after thebombardment. Our results illustrate that the field emission characteristicswere improved after the bombardment of N+2.

XPS characterization of the composition and bonding states of elements in CNx layers prepared by ion beam assisted deposition

CNx layers were grown on polished Si(100) wafers by the ion beam assisted deposition (IBAD) technique at temperatures varying between 200 and 600 °C. A Kaufman type ion source fed by Ar and N2 was applied together with an e-beam heated evaporation source of graphite for the deposition of the CNx layers. The composition and chemical bonding state of elements were studied by X-ray photoelectron spectroscopy. The N-content varied in the range of 8–16 at.% and showed a decrease with the increase of deposition temperature. The broad C1s and N1s XPS lines manifested several bonding states. The relative intensities of the component peaks varied with the preparation conditions. The two main components of the N1s peak situated at BE=398.2 eV and 400.6 eV were assigned to sp2 (CNC) and sp3 (NC) type bonding states, respectively. The thermal stability of the sp3 states was higher than that of the sp2 ones, because the intensity of the 398.2 eV component decreased preferentially with increasing deposition temperature. A post-deposition treatment with low energy N2+ ion beam resulted in a significant increase in the overall N-content on the surface, with a preferential increase in the concentration of sp2 type nitrogen.

Interstitial nitrogen induced by low-energy ion beam nitridation of AIII–BV semiconductor surfaces

The nitridation of GaAs, InAs, and InSb by low-energy N2+ ion bombardment at room temperature was studied by near-edge x-ray absorption fine structure (NEXAFS) and x-ray photoelectron spectroscopy measurements. The formation of thin surface nitride layers, consisting mostly of GaN or InN but also containing minor amounts of mixed nitrides, was observed. Besides the nitride-related features, sharp peaks in the NEXAFS due to π* resonance at 401.0 eV and correlated peaks at 403.8 eV in N 1s core level spectra were detected. Both spectral features could be assigned to the presence of interstitial nitrogen, most likely molecular nitrogen. It was found that the amount of interstitial nitrogen in the surface layer strongly depends on the AIII–BV semiconductor system and may be affected by modification of the conditions during low energy ion bombardment.

Near edge x-ray absorption fine structure spectroscopy study of atomic nitrogen implanted in Al2O3 by low energy N2+ bombardment

N 2 + bombardment of Al2O3 has been investigated by near edge x-ray absorption fine structure spectroscopy. Two kinds of species were detected and were attributed to implanted nitrogen atoms and nitride species. These results are discussed in relation to previous attributions in the literature of these species to AlNO and AlN.

The quantum world of cold electron collisions.

Collisions between electrons and molecules at thermal energy play a key role in the chemistry and physics of plasmas, ranging from those in space to the chemically active plasmas used for thin film and microcircuit fabrication. However, until recently, data for electron-molecule interactions below a few hundred millielectronvolts impact energy (a few thousand kelvin) were very sparse. Our experiments, using a high-resolution synchrotron photoionization source of electrons, have opened up this low-energy field. We present recent results which reveal some of the striking quantum scattering events which take place as long-wavelength, low-energy electrons encounter molecules, choosing H(2), N(2), benzene, halobenzenes, methanol, ozone, and chlorine dioxide as examples.

Surface chemical effects of low-energy N2+ ion bombardment on single crystalline ?-Al2O3

Composition changes and chemical structure alterations initiated by ion beams on metal oxide surfaces have been widely studied. Significant differences in the effect of low-keV inert (Ar+) and reactive (N2+) ion impact on a series of metal oxides have been published recently by the present authors. In this work the effect of 0.5–5 keV N2+ bombardment on single crystalline α-Al2O3 was studied by quantitative XPS. Clarifying the existing ambiguity, experimental evidence is presented that supports the preferential oxygen loss and build-up of nitrogen. The oxygen loss increased with increasing N2+ ion energy until approaching an atomic ratio saturation value of O/Al ∼1 on 3.5 keV bombardment with the concomitant build-up of N at N/Al ∼0.5. In contrast to other oxides, for α-Al2O3 two major types of nitrogen were detected on N2+ impact; the two N 1s lines were separated by 7 eV. The one at 396.4 eV binding energy corresponds to a nitride-type N–Al environment, similar to that found in bulk AlN. Formation of the nitride is interpreted as the result of replacement of lattice oxygen around Al by implanted nitrogen in a two-stage process. The 403.4 eV component is assigned to nitrogen trapped in the cation-deficient lattice of α-Al2O3 in empty octahedral sites surrounded by oxygen atoms bonded to Al. Both of these chemical states of nitrogen were stable on heating up to 550–650 °C. Copyright © 2000 John Wiley & Sons, Ltd.