Narrow Nuclear Resonance Profiling Research Articles

Direct measurement of molecular breakup dynamics and vicinage effect of swift proton clusters using narrow nuclear resonance profiling

We report on the first direct observation of the evolution with time of the vicinage effect and Coulomb explosion for H 2 + and H 3 + molecules in a thick amorphous silica layer enriched with 18O atoms. High depth resolution is achieved by using the 18O ( p, α) 15N nuclear reaction narrow resonance around E R = 151 keV/nucleon (corresponding to a velocity V), and scanning the beam energy around E R . The results are well described when using a Coulomb screening radius r s ≈ (2/ π) R ad where R ad = V/ ω p is an adiabatic cut-off for a valence electron gas with plasmon frequency ω p ≈ 24 eV. The vicinage effect is reproduced when describing the experimental energy loss function of the target valence electron gas by a single Drude function with damping factor γ ≈ 22 eV and including multiple scattering on target nuclei.

Thermal oxidation of 6H-SiC studied by oxygen isotopic tracing and narrow nuclear resonance profiling

We show that on SiC ( 0 0 0 1 ̄ ) (the fast-oxidizing carbon face), at 1100 °C and 100 mbar, the oxide exhibits an initial fast growth regime, followed by a constant growth rate confirming previous results that oxide growth is not limited by diffusion of the oxidizing species or reaction products through the oxide. At 1100 °C, in this linear regime, the growth rate also exhibits a linear dependence with oxygen pressure. The silicon face shows sub-linear pressure dependence. A simple oxidation model is ruled out since, on both SiC faces, sequential 16O 2/ 18O 2/ 16O 2 oxidations show that oxygen fixed in the oxide, near the SiC/SiO 2 interface moves during subsequent growth.

Enhanced initial growth of atomic-layer-deposited metal oxides on hydrogen-terminated silicon

A route is presented for activation of hydrogen-terminated Si(100) prior to atomic layer deposition. It is based on our discovery from in situ infrared spectroscopy that organometallic precursors can effectively initiate oxide growth. Narrow nuclear resonance profiling and Rutherford backscattering spectrometry show that surface functionalization by pre-exposure to 108 Langmuir trimethylaluminum at 300 °C leads to enhanced nucleation and to nearly linear growth kinetics of the high-permittivity gate dielectrics aluminum oxide and hafnium oxide.

Thermal behavior of hafnium-based ultrathin films on silicon

We report here on the thermodynamical stability of ultrathin, hafnium-based dielectric films, namely hafnium oxide (HfO2), silicate (HfSixOy), and aluminum silicate (AlHfxSiyOz), deposited on silicon. These materials are promising candidates to replace the well established silicon oxide and oxynitride as gate dielectric materials in advanced Si-based complementary metal–oxide–semiconductor technology. Since there are mandatory requirements on the gate dielectric material, hafnium oxide is currently being modified, by adding silicon and aluminum into the matrix, increasing its thermal stability, and improving its electrical properties. Diffusion-reaction during thermal processing was investigated using isotopic substitution together with ion beam techniques such as Rutherford backscattering spectrometry, narrow nuclear resonance profiling, and nuclear reaction analysis. The chemical changes in the films were accessed by x-ray photoelectron spectroscopy.

Depth resolution and narrow nuclear resonance profiling

Abstract The basic stochastic theory of narrow nuclear resonance profiling is presented. We show that nm depth resolution is achievable in some cases. It is shown that the usual notions of depth resolution such as the full width at half maximum of the instrument function, adequate for instrument functions which vary only slowly over the depth range corresponding to the depth resolution, are unsatisfactory for narrow resonance profiling in the near surface region. Here, the system response to a delta function concentration profile varies very rapidly. However, the shape of the excitation curve is very sensitive to certain kinds of small changes in the concentration profile in the surface region. We discuss some first efforts to define a more general concept for depth resolution, consistent with the usually used definitions, intended to adequately express the perceived sensitivity of a measured excitation curve to variations in the underlying concentration profile.

SURFACE AND INTERFACE INVESTIGATION OF NANOMETRIC DIELECTRIC FILMS ON Si AND ON SiC

Dielectric films on Si or SiC were investigated using angle-resolved X-ray photoelectron spectroscopy (ARXPS) and ion beam analysis techniques, namely high and low energy ion scattering (RBS and LEIS) and narrow nuclear resonance profiling (NRP) combined with isotopic substitution. For the Si substrate, attention was focused on the thermal stability of materials candidate to replacing SiO 2 in Si-based microelectronic devices (so-called "high-k dielectrics"): Al 2 O 3, ZrSi x O y, ZrAl x O y, HfSi x O y, and GdSi x O y. Mobility of different atomic species — especially Si and O — was observed at both the surface of the films and the interface with Si. Such atomic transport may have serious consequences concerning application of these materials in the microelectronics industry. For the SiC substrate, attention was focused on the initial stages of thermal oxidation in O 2, seeking an understanding of its poorer electrical quality as compared to SiO 2– Si . It was found that the initial oxidation products are silicon oxycarbides ( SiC x O y), while for longer oxidation times a mixture of SiC x O y and SiO2 is formed in the near surface region of the growing film. The composition of the near surface region of such thin films is very similar to that reported in previous investigations for the near interface region when thicker oxides films are grown on SiC.

Ion beam studies of high- k ultrathin films deposited on Si

The stability of ultrathin films on Si, which are materials candidates for replacing SiO 2 in Si-based microelectronic devices (so-called “high- k dielectrics”), was investigated using ion beam analysis techniques, namely high and low energy ion scattering (RBS and ISS) and narrow nuclear resonance profiling combined with isotopic substitution. The materials studied were Al 2O 3, ZrSi x O y , HfSi x O y , AlZr x O y and GdSi x O y . The mobility of different atomic species – especially Si and O – could be observed upon thermal annealing, involving the surface, bulk and interface regions of the films. These atomic transports may have serious consequences concerning application in the microelectronics industry. The potentialities and limitations of each of the IBA methods used are discussed.

Narrow nuclear resonance profiling of Al with subnanometric depth resolution

We report on the use of the narrow and isolated resonance at 404.9 keV in the cross-section curve of the 27 Al(p,γ) 28Si nuclear reaction for profiling Al in ultrathin aluminum oxide films on Si. The samples were characterized as-deposited and after thermal annealing, so that Al transport could be studied. An estimated depth resolution of approximately 0.4 nm near the surface of the films could be obtained owing to: (i) the very small resonance width; (ii) the high stopping power of Al 2O 3 for 404.9 keV protons; (iii) the high energy stability of the proton beam provided by the 500 kV HVEE ion implanter at Porto Alegre; and (iv) an apparent thickness magnification by a factor between 2.0 and 2.4 with the use of glancing incidence. This technique is compared to other methods for Al profiling like medium energy ion scattering and some sputtering-based techniques.

Annealing of ZrAlx O y Ultrathin Films on Si in a Vacuum or in O 2

films deposited on Si were submitted to thermal annealings in a vacuum or an oxygen atmosphere. Elemental compositions as functions of depth were established using ion beam techniques such as Rutherford backscattering spectrometry and narrow nuclear resonance profiling. In addition, chemical composition profiles were obtained by angle-resolved X-ray photoelectron spectroscopy. The as-deposited film is amorphous, has an abrupt interface with the Si substrate, and its chemical composition is a double oxide with approximate stoichiometry Atomic transport and chemical reaction induced by thermal annealing were investigated by the above mentioned techniques and by low energy ion scattering spectroscopy. We have observed that Al, O, and Si migrate during annealing, whereas Zr is essentially immobile. Oxygen from the gas phase was heavily incorporated into the oxide films during annealing in mostly in exchange for previously existing oxygen. © 2001 The Electrochemical Society. All rights reserved.

Composition, atomic transport, and chemical stability of ZrAlxOy ultrathin films deposited on Si(001)

The stability of a ZrAlxOy film sputtered on Si upon thermal annealing in vacuum or in O2 was investigated. X-ray diffraction indicated that the as-deposited film was amorphous and remained so after annealing. Rutherford backscattering, narrow nuclear resonance profiling, and low-energy ion scattering provided the average composition of the film and the depth distributions of different elements. Chemical analysis of these elements was accessed by x-ray photoelectron spectroscopy. Annealing in vacuum produced thickness inhomogeneities and/or transport of very small amounts of Si from the substrate into the overlying film, with formation of Si precipitates. Annealing in O2 led to oxygen exchange throughout the film, as well as Si transport in slightly higher amounts than in vacuum. Differently from the observed upon annealing in vacuum, Si was either incorporated into the Zr,Al–O framework or oxidized in SiO2.

Stability of zirconium silicate films on Si under vacuum and O2 annealing

The effect of postdeposition annealing in vacuum and in dry O2 on the atomic transport and chemical stability of chemical vapor deposited ZrSixOy films on Si is investigated. Rutherford backscattering spectrometry, narrow nuclear resonance profiling, and low energy ion scattering spectroscopy were used to obtain depth distributions of Si, O, and Zr in the films. The chemical environment of these elements in near-surface and near-interface regions was identified by angle-resolved x-ray photoelectron spectroscopy. It is shown that although the interface region is rather stable, the surface region presents an accumulation of Si after thermal annealing.

Low energy nitrogen implantation into Si and SiO 2/Si

We report on N doses and profiles in Si and (ultra)thin SiO 2 films on Si nitrided by plasma or ion beam processing in the 3–1000 eV energy range. Accurate elemental quantification was performed by nuclear reaction analysis (NRA), and elemental profiling with subnanometer depth resolution was achieved by narrow nuclear resonance profiling (NNRP) or medium energy ion scattering (MEIS). Heavy and shallow nitrogen incorporation was observed up to 0.7 N/(N + O) and peak N concentrations at 2 nm and less from the sample surface. Device-quality films were produced with post-nitridation annealing in O 2, as indicated by C– V and I– V measurements.

Isotope-beam modification of materials at eV energies

We developed a low energy ion beam deposition system for isotope-selective modification of materials. It consists of a conventional ion implanter (HVEE 500 kV) and an attachable deceleration system. 29(N 2) + ion beams were used for the nitridation of Si(0 0 1) and the resulting 15N retained doses and profiles were determined by narrow nuclear resonance profiling. 29Si was deposited on amorphous carbon films on Si(0 0 1) and the doses evaluated by channeled α particle beams with detection of scattered α at grazing angles. 29Si was also deposited on Si(0 0 1) and the resulting profiles determined by narrow nuclear resonance.

Very low energy nitrogen implantation for ultrathin silicon oxynitride film formation

We investigated the influence of the surface concentration of N (in the range 1/30–1 monolayer) on the thermal growth rate of silicon oxide films. Very low energy (20 eV) 15N + ions were implanted onto Si(1 0 0) substrates and thermal oxidations were performed in 18O 2. In some samples N deposition was performed on an 8 nm thick 29Si layer also deposited by low energy ion implantation on natural Si. The amounts of N and O in the films were determined by Nuclear Reaction Analysis (NRA), and the N, O, and Si profiles were determined with nanometric depth resolution by narrow nuclear resonance profiling. A progressive reduction of the oxidation rate with the increase of the areal density of N was observed. Isotopic tracing revealed the details of the redistribution of N in the films and its effects on the mechanisms of thermal growth of the dielectric layer.

Effects of the surface deposition of nitrogen on the thermal oxidation of silicon in O2

Nitrogen was deposited on the surface layers of Si(100) by ion implantation at a very low energy (approximately 20 eV), at fluences between 1 and 10×1014 cm−2. The samples were thermally oxidized in dry O2 at 1050 °C, and the areal densities and profiles of N and O were determined by nuclear reaction analysis and narrow nuclear resonance profiling, evidencing that: (i) the retained amounts of N just after ion beam deposition stayed in the range between 0.3 and 7×1014 cm−2; (ii) the oxide growth is influenced strongly by the presence of nitrogen, the thickness of the oxide films (which remained between 4 and 30 nm) decreased with the increase of the areal density of nitrogen; (iii) N is partially removed from the system as oxidation proceeds. These observations are discussed in terms of current models for the thermal growth of silicon oxide in the presence of N.