Ion Channeling Techniques Research Articles

Lattice Location of Boron and Hafnium Dopants in an Aluminide by Use of Ion Channeling/Nuclear Reaactnio Analyses

AbstractExperiments have made use of Rutherford backscattering (RBS), ion channeling techniques and analyses for nuclear reaction products to study lattice location of B and Hf dopantsin an ordered nickel aluminide. Studies were of an alloy single crystal of composition Ni76A123Hf1 with about 0.1 at. % of B added. Analysis for B was accomplished by detection of alpha particles resulting from the reaction 11B(p,αi)8 Be, in ion channeling experiments in which RBS from the Ni constituent was used to control channeling in the host lattice. Yield of the reaction product from proton interaction with B decreased relative to random for channeling in a <100> direction, but increased relative to random for channeling in a <110= direction. It was concluded that B occupies primarily octahedral interstitial sites. RBS/channeling half-angles for Hf in a <100> direction are somewhat smaller than those for Ni, but nevertheless considerably larger than half-angles expected for Al. It is concluded that the majority of Hf atoms are on the Ni sublattice.

High resolution studies of NiSi 2 ultrathin film formation by ion scattering and cross-section tem

Ultrathin epitaxial NiSi 2 films (0–40 Å) have been grown on Si(111) surfaces. Medium energy ion shadowing and blocking has been used to determine the orientation, morphology and interfacial order of these films. For the whole coverage range studied ((0–1) × 10 16 Ni atoms cm 2 ) the films are found to be rotated 180° about the surface normal with respect to the Si(111) substrate. Using the high depth resolution of the technique the annealed films are shown to consist initially of islands, which coalesce into continuous films for coverages above ≈ 5 × 10 15 Ni atoms cm 2 . High resolution cross-section transmission electron microscopy shows the NiSi 2Si interface to be atomically abrupt. This interface has been probed directly using the ion channeling technique, and the number of disordered Ni atoms at the interface is found to be less than 7.5 × 10 13 atoms cm 2 .

Thermal stability of trapped interstitials in Al(Ag)

The thermal stability of trapped interstitials in an irradiated Al-0.09 at.% Ag crystal was studied using the ion channeling technique. The fraction f〈lmn〉dAg of Ag atoms displaced from substitutional lattice sites into 〈lmn〉 channels was monitored, using backscattering of 1.0 MeV 4He ions, for 〈110〉 and 〈100〉 axial alignment as well as for an orientation 0.4° from the 〈110〉 axis. Irradiations at 70 K with 1.0 MeV 4He ions resulted in an appreciable fraction of the Ag atoms being displaced from lattice sites (particularly into 〈110〉 channels) when migrating interstitial atoms were trapped at the Ag atoms. For irradiation fluences up to ∼ 6 × 10 15ions cm −2, the 〈100〉 mixed dumbbell was the most prevalent trapping configuration. At higher ion fluences, however, the results indicated that there was a gradual change in the trapping configuration. The change in configuration was attributed to the trapping of more than one self-interstitial at each Ag atom.Annealing experiments were performed following 70 K irradiations with 1.0 MeV 4He ions to fluences ranging from 1.2 × 10 15 to 29.3 × 10 15 ions cm −2. At the lowest irradiation fluence of 1.2 × 10 15 ions cm −2 essentially no change in f〈lmn〉dAg (or in the trapping configuration) occurred during annealing from 70 to 170 K. However, f〈110〉dAg and f〈100〉dAg decreased in the temperature range 170 to 230 K; at 230 K nearly all of the Ag atoms returned to substitutional sites. The irradiation-induced dechanneling increment (a measure of the total defect concentration) also annealed out between 170 and 230 K. The results indicated that the trapping configuration was changing in the region 170 to 230 K, which suggested that the annealing mechanism involved more than simply the annihilation of a migrating monovacancy with the self-interstitial atom trapped in the mixed dumbbell configuration. As the irradiation fluence was increased, there was a downward temperature shift of the stage in which vacancies were annihilating with trapped interstitial atoms, presumably due to the higherconcentration of defects present. In addition, a noticeable recovery f〈110〉dAg occurred below ∼ 110 K, hence indicating a more complex annealing behaviour when multiple trapping of the self-interstitial atoms at Ag atoms occurred initially.

Vacancy trapping in Cu-0.1 at.% In

Perturbed angular correlation (PAC) and ion channelling techniques were used to study the trapping of vacancies by In atoms in a Cu-0.13 at.% In crystal after H+ irradiation. Four major defect complexes were observed; the fractions f1, f2, f7 and fT of In atoms which were associated with these complexes were measured as a function of annealing temperature and irradiation fluence. The complexes f1, f2 and f7 were observed only by the PAC technique; the coupling constants for these defects were vQ1=116 MHz, vQ2=181 MHz and vQ7=106 MHz, all having eta =0. The first two of these had previously been shown to be due to trapping of one and two vacancies. The third may be due to He trapping. A tetrahedral complex fT, consisting of an In atom in the tetrahedral interstitial site surrounded by four nearest-neighbour vacancies was observed by channelling but was invisible by the PAC method. Complexes, f1, f2, and fT were formed during annealing from 180-250K. The fractions f1 and f2 decreased strongly during annealing from 250-230K, while the tetrahedral complex was stable up to approximately 500K. The complex f7 appeared during annealing above 320K and continued to increase up to 600K. The fractions f1, f2 and fT were all reduced during 70K irradiations by the absorption of self-interstitial Cu atoms.

Observation of two-dimensional ordering in ion-damaged graphite during post-implantation annealing

Post-implantation annealing of ion-damaged, highly oriented pyrolytic graphite has been studied by Raman spectroscopy, ion-channeling techniques, and transmission electron microscopy. Complementary information obtained by these methods provides confirmation for the first step of graphitization of ion-damaged graphite at annealing temperatures of \ensuremath{\sim}2300\ifmmode^\circ\else\textdegree\fi{}C. This is manifested by the formation of carbon planes with two-dimensional ordering but no correlation in the third ($c$-axis) dimension.

Heavy ion induced damage and annealing processes in silicon

Heavy ion damage in silicon has been investigated by ion channeling and transmission electron microscopy techniques. Implantation temperatures between 77 K and 720 K have been employed. Our results suggest that significant annealing of displacement damage can take place during implantation at temperatures as low as 77 K. Important differences in the amount of damage are observed in (100) and (111) substrates. For elevated temperature implantations, our results suggest a new mechanism for amorphous phase production.

Comment on ‘‘Lattice location of chromium in semi-insulating GaAs by ion channeling techniques’’ [Appl. Phys. Lett. 4 2, 599 (1983)

A comment on lattice location of chromium by ion channeling and detection of x-ray signals of Cr-Kα excited by 1-MeV H+ from a Cr-doped GaAs is presented.

Damage effects in silicon and MNOS structures caused by beams of ionized and neutral argon atoms with energies below 5 keV

Low energy ion and/or atom beams (2–5 keV) produced by saddle field ion sources have been used to study the damage effects of ion/atom beam milling on single crystal silicon wafers either uncoated or with both thermal oxide and deposited silicon nitride layers on the surface. MeV ion channelling techniques and transmission electron microscopy have been applied to assess the total disorder, argon retention and microstructure of the damage in the uncoated wafers before and after annealing. Capacitance voltage measurements (1.3 MHz and quasi-static) have been made on MNOS structures after ion and atom beam milling. Specimens bombarded with atoms show smaller flatbed shifts than those bombarded with ions of the same energy and dose. The results are interpreted in terms of field assisted injection of charge carriers during bombardment and preferential removal of positive space charge (holes) during low temperature annealing.

Microstructure investigation of initial formation of the Pd2Si-Si interface by TEM and ion channeling techniques

Recent synchrotron-radiation experiment have established that the formation of the Schottky barrier at some transition metal-Si interface is essentially completed upon metal deposition of the first few monolayers. One problem of basic importance is the structural morphology and metal atom distribution of the initial silicide-Si interface. To complement our studies on the electronic and electrical characteristics, transmission electron microscopy (TEM), reflection electron microscopy (REM) and ion channeling techniques were used to investigate the microstructure of the initial Pd2Si-Si interface.Samples were prepared in UHV chember by e-beam evaporation of about 30-80 Å Pd on Si (100) or (111) substrates at room temperature then annealed at 200°C in various times to form Pd2Si. Back-etching of the Si substrates was finished with CP-4 solution. Samples were examined using a JEOL 200 CX microscope with TEM and REM mode.Fig. 1 is a high resolution lattice image of Pd2Si on (111) Si and a diffraction pattern. The amount of Pd deposited was estimated to be 80Å by ion back scattering

Lattice location of chromium in semi-insulating GaAs by ion channeling techniques

Proton-induced x-ray emission combined with ion channeling techniques has been used to investigate the lattice location of Cr in GaAs grown by the Czochralski method. The angular dependence of Cr x-ray yields about the 〈100〉 and 〈110〉 directions indicated that the Cr atoms occupied the substitutional sites with no trace of well-defined Cr interstitials at the concentrations studied. Fe and Ni impurities in Cr-doped GaAs were located at the substitutional sites whereas Cu impurities were more likely distributed among random sites with respect to the host atoms.

Two-Dimensional Ordering of Ion Damaged Graphite

ABSTRACTPost implantation annealing of ion-damaged, highly oriented pyrolytic graphite (HOPG) has been studied by Raman spectroscopy, the ion channeling technique and Transmission Electron Microscopy. Complementary information obtained by these methods provides confirmation for the completion of the first step of graphitization of iondamaged graphite at annealing temperatures of ~2300°C. This is manifested by the formation of carbon planes with two dimensional ordering but no correlation in the third (c-axis) dimension.

Superlattice Interface and Lattice Strain Study by Ion Channeling

EXTENDED ABSTRACTWe have studied the interface and the lattice strain of superlattices by ion channeling technique. The objective in this work is to verify the existence of alternating tensile and compressive strain in the superlattice and to develop a method for measuring the lattice strain directly. Alternating layers of GaSb/Al Sb were grown epitaxially by MBE with 10 periods. The thickness of each individual layer is 30 nm. Channeling measurements and analysis were made using a 1.76 MeV 4He ion beam. The measurements reveal higher dechanneling along the [110] axis than along the [100] axis. This is consistent with the dechanneling results published earlier. The high dechanneling along the [110] axis has been considered due to the lattice strain that occurs in the layers caused by the slight mismatch between the lattice constants of the two materials. The strain effect make [110] axis slightly bent from layer to layer (“zigzag”), but it does not occur in [100] axis. The axial angular scan analyses were made around the [110] direction at the different depths using a movable energy window setting. We have found that the angular position of the best alignment shifts from layer to layer. The oscillation of those angular positions with depth is of a direct evidence of the existence of alternating tension and compression strain layers in the superlattice. The “kink” angle at the interface is given by the difference of the angular position between the first and second layer. This is found to be 0.17° ± 0.03 %. This is in a good agreement with the result calculated from elasticity. Preliminary result of this experiment is recently published.3We are also investigating the interface and lattice strain by planar angular scan across the (110) plane at a position three degrees from [110] axis.The similar oscillatory results have been found for {110} planar channeling and the “kink” angle measurement is in a good agreement with the results from axial angular scan.We believe that the method of ion beam channeling and angular scan is very effective in strain measurements in multi-layered heteroexpitaxy system.3. W. K. Chu, C. K. Pan and C.-A. Chang, Phys. Rev. Rapid Communication B28, 4033 (1983).

Development of morphological instability and formation of cells in silicon alloys during pulsed laser irradiation

The details of morphological instabilities occuring during rapid solidification have been studied in In +, Sb +, Ga + and Bi + implanted silicon after pulsed laser annealing. Interfacial instability results in lateral segregation of impurities, which leads to the formation of cellular structures. The average cell sizes, at the onset of instability (OI) and in the region of well-developed instability (DI), were determined using plan-view and cross-section electron microscopy. Total and substitutional solute concentration profiles were determined using high resolution Rutherford backscattering, ion channeling techniques. The formation of cells and the critical solute concentrations associated with instability were studied as a function of velocity of solidification by varying either the substrate temperature or the laser parameters. Results on the cell formation and the critical solute concentrations were compared with calculations of the perturbation theory in which experimentally deduced values of distribution coefficients and liquids slopes were used. A good agreement was obtained between the calculations and the ecperimental results on critical solute concentrations, and between the calculations and the OI cell sizes, which were larger than those in the DI region.

Redistribution of As during Pd2Si formation: Ion channeling measurements

We have investigated the redistribution of As during Pd2Si formation with ion channeling technique. The results show that both interstitial As and substitutional As in the Si are pushed ahead by the moving silicide-silicon interface during the growth of Pd2Si at 250 °C. This effect increases the As concentration in a region of about 100 Å beyond the interface. A model for the mechanism of As redistribution during silicide formation is suggested and implications of the effect on electrical characteristics of Schottky diodes and shallow junction devices are discussed.

Non-planar solid phase epitaxial growth processes in ion-implanted GaAs

High resolution ion channelling and reflection electron diffraction techniques have been used to examine details of epitaxial regrowth in Ar +-ion-implanted GaAs(100) at furnace anneal temperatures of 400°C or less. In particular, we have investigated the nature and extent of epitaxial regrowth during both isothermal and isochronal annealing for various implant energies and for implant doses above and below the amorphous threshold. Our results indicate the development of a non-planar growth interface during annealing which may lead, ultimately, to complex near-surface crystallization processes. Consistently with our observations and recent results from other laboratories, we propose a model for the epitaxial regrowth of amorphous GaAs layers based upon non-uniform growth rates along the amorphous-crystalline interface which could arise from local stoichiometry imbalance.

Electronic states and microstructure at the silicide-silicon interface

The understanding of Schottky barrier formation at the silicide-silicon contact requires information on the electronic states and microstructure of the reacted interface. Considerable progress has been made recently in the study of these interface properties using surface spectroscopy, transmission electron microscopy and ion channeling techniques. This review is focused mainly on the results for the near-noble metal silicides with some brief discussions for the refractory metal silicides. The basic bonding characteristics in silicides are discussed first with emphasis on the role of hybrid states between metal d and Si p orbitals. Then the stoichiometry and microstructure of the interface as well as their effect on the electronic properties are described. Spectroscopy evidence is given to show the existence of interface states in the vicinity of the band gap. Finally, measurements of Schottky barrier height are discussed in an attempt to assess the effects of phase stoichiometry and microstructure on the electrical properties of the Schottky barrier.

Channeling study of low- Z impurities dissolved in metals

The lattice location of low- Z impurities dissloved in metals was studied in bcc (D in Ta, O in V, Al and Si in Cr) and fcc (D in Pd 0.8Au 0.2) host lattices by the ion channeling technique in connection with nuclear reactions or ion induced X-rays. In order to detect low- Z impurities, we used the following nuclear reactions: D(d, p)T, D( 3He, p) 4He for VD 0.01, NbD 0.01, TaD 0.01, TaD 0.10 and Pd 0.8Au 02D 0.04; 16O(d, p) 17O ∗ for VO 0.01, VO 0.02, ZrO 0.33 and NbO. The proton induced X-rays were used for CrAl 0.014 and CrSi 0.024. The site was found to be tetrahedral for D in Ta, octahedral for O in V, octahedral for D in Pd 0.8Au 0.2 and substitutional for Al and Si in Cr. D atoms implanted into Pd 0.8Au 0.2 occupy octahedral sites at 25 K, random positions at 110 and 150 K. The thermal vibrations of D, the O concentration dependence for channeling behaviour and the D trapping by radiation induced defects are described.

Cell formation and interfacial instability in laser-annealed Si-In and Si-Sb alloys

The formation of cellular structures resulting from interfacial instability has been studied in indium- and antimony-implanted silicon after pulsed ruby laser annealing. The average cell sizes at the onset of instability and in the region of well-developed instability were determined using cross-section and plan-view electron microscopy, while the Rutherford backscattering ion-channeling technique was used to obtain solute concentration profiles. These results on average cell sizes and solute concentrations were compared with the predictions of the perturbation theory, which included the dependence of distribution coefficient on the velocity of solidification.

Electrical and structural characterization of implantation doped silicon by infrared reflection

Abstract A physical model is presented for calculating infrared reflection interference spectra from ion implanted and annealed crystalline materials. The utility of the method is illustrated by presenting best fit spectra for a <111> silicon sample implanted with 2.7 MeV phosphorous to a fluence of 1.74 × 1016 ions/cm2 and isothermally annealed at 500°C. Non-linear least-squares fitting of reflection data yields structural and electrical information about the implanted region with reasonable precision. The physical quantities determined are (i) the depth of the amorphous layer produced by implantation both before and during isothermal annealing, the thickness of the recrystallized material, and the widths of any transition regions, (ii) the dielectric properties of the amorphous and recrystallized material, and (iii) the characteristics of the free carrier plasma which yield the carrier density profile, the mobility near the carrier density maximum, and the carrier activation efficiency. Up to nine fitting parameters are necessary to describe these physical quantities. A critical discussion of the sensitivity of data fit to variation in the parameters is given to establish the uniqueness of fitted parameters. The infrared method is non-destructive, is applicable to other dopants and semiconductors, and provides information complementary to both ion channeling and resistivity profiling techniques.

Non-Planar Solid Phase Epitaxial Growth Processes in Ion-Implanted GaAs

High resolution ion channelling and reflection electron diffraction techniques have been used to examine details of epitaxial regrowth in Ar+-ion-implanted GaAs(100) at furnace anneal temperatures of 400°C or less. In particular, we have investigated the nature and extent of epitaxial regrowth during both isothermal and isochronal annealing for various implant energies and for implant doses above and below the amorphous threshold. Our results indicate the development of a nonplanar growth interface during annealing which may lead, ultimately, to complex near-surface crystallization processes. Consistently with our observations and recent results from other laboratories, we propose a model for the epitaxial regrowth of amorphous GaAs layers based upon non-uniform growth rates along the amorphous-crystalline interface which could arise from local stoichiometry imbalance.